Dissertations / Theses on the topic 'Optoelectronic transistors'
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1
Bird, Matthew J. "Optoelectronic processes in polyfluorene ambipolar transistors." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/256013.
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This thesis describes the use of charge modulation spectroscopy to investigate the negative and positive charge-induced absorptions in conjugated semiconducting polymers as a way to experimentally compare the wavefunctions of electrons and holes. Interactions between light and charges including fluorescence quenching and photocurrent are also explored. Conjugated polymers have an electronic structure with an energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). In the neutral ground state, there are no optical transitions at photon energies lower than this gap. When an excess charge is added to a conjugated polymer, the charge couples with a local structural reorganisation forming a localised entity known as a polaron. The polaron has two new electronic states within the energy gap symmetrically spaced about the midgap energy. Typically two new optical transitions between the polaronic states are allowed and can be accessed with sub gap energies. In order to probe the sub gap polaron absorptions charges can be added by electrical injection. Electrical injection in a transistor configuration provides a controlled way to measure the absorption of a known number of charges in the solid state and without triplet or singlet absorptions complicating the spectra as observed in photo-induced absorption. By taking advantage of recently developed ambipolar transistors where both holes and electrons can be accumulated in the same device a comparison can be made between the negative and positive polaron wavefunctions. Two polyfluorene polymers were chosen as examples where quantum chemical calculations predict either the same or different wavefunctions for the electron and hole. Poly(9,9-di-n-octylfluorene) (F8) is a hydrocarbon-only polymer which is expected to have similar electron and hole wavefunctions, whereas the related co-polymer, poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) is expected to have an electron wavefunction that is more localized that the hole. The ambipolar transistors used in this thesis are typified by a dominant contact resistance which introduces difficulties in the charge modulation spectroscopy experiment. New techniques for simultaneous electrical and optical characterisation are developed and new device structures and fabrication processes are introduced in order to overcome a number of artifacts and improve the accuracy of the measurement allowing quantitative comparisons to be made. The increase in transistor or diode current with energy gap illumination and the quenching of fluorescence in the presence of charges is also investigated and a new method for imaging charge trapping and device operation in transistors with luminescent semiconductors is introduced.
2
Liu, Chin Pang. "Optoelectronic mixing in heterojunction bipolar transistors." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312033.
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Huang, Yong. "InAlGaAs/InP light emitting transistors and transistor lasers operating near 1.55 μm." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37298.
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Light emitting transistors (LETs) and transistor lasers (TLs) are newly-emerging optoelectronic devices capable of emitting spontaneous or stimulated light while performing transistor actions. This dissertation describes the design, growth, and performances of long wavelength LETs and TLs based on InAlGaAs/InP material system. First, the doping behaviors of zinc (Zn) and carbon (C) in InAlGaAs layers for p-type doping were investigated. Using both dopants, the N-InP/p-In0.52(AlxGa1-x)0.48As/N-In0.52Al0.48As LETs with InGaAs quantum wells (QWs) in the base demonstrate both light emission and current gains (β). The device performances of Zn- and C-doped LETs have been compared, which is explained by a charge control analysis involving the quantum capture and recombination process in the QWs. A TL based on a C-doped double heterostructure (DH-TL) with single QW was designed and fabricated. The device lases at 77 K with a threshold current density (Jth) of 2.25 kA/cm2, emission wavelength (λ) at ~1.55 µm, and β of 0.02. The strong intervalence band absorption (IVBA) is considered as the main intrinsic optical loss that prohibits the device from lasing at room temperature. Based on a threshold condition analysis taking into account the strong IVBA, it is found that room-temperature lasing of a DH-TL is achieved only when the base thickness and doping level are within a specific narrow range and improved performance is expected in a separate confinement heterostructure (SCH) TL.
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Loga, Rodney Izzat. "HBT/DHBTs for monolithic optoelectronic interfaces." Thesis, King's College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268719.
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Tan, Eugene. "Design, fabrication and characterization of N-channel InGaAsP-InP based inversion channel technology devices (ICT) for optoelectronic integrated circuits (OEIC), double heterojunction optoelectronic switches (DOES), heterojunction field-effect transistors (HFET), bipolar inversion channel field-effect transistors (BICFET) and bipolar inversion channel phototransistors (BICPT)." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0006/NQ42767.pdf.
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Ho, Kai Wai. "Evaluation and characterization of efficient organic optoelectronic materials and devices." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/816.
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With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.
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Ho, Ka Wai. "Evaluation and characterization of efficient organic optoelectronic materials and devices." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/873.
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With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.
8
Fiebig, Matthias. "Spatially resolved electronic and optoelectronic measurements of pentacene thin film transistors." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-122033.
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Unal, Selim. "Field-effect transistors and optoelectronic devices based on emerging atomically thin materials." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/27140.
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Development of field-effect transistors and their applications is advancing at a relentless pace. Since the discovery of graphene, a single layer of carbon atoms, the ability to isolate and fabricate devices on atomically thin materials has marked a paradigm shift in the timeline of transistor technologies. In this thesis, electrical and optical properties of atomically thin structures of graphene and tungsten disulfide (WS2) are investigated. Transport in graphene side-gated transistors and contact resistance at the metal-WS2 interface are presented. Finally, the optoelectronic performance of the hybrid graphene-WS2 devices is examined. Presently, atomically thin semiconductors grown by chemical vapour deposition are of growing interest by a broad scientific community. For this work of thesis, an air stable material which requires non-toxic gases for the growth such as WS2 is selected. A considerable contact resistance at the metal/WS2 interface is found to hamper the electrical performance of WS2 transistors. The possible origin of this contact resistance is presented in this thesis. The graphene field-effect transistors with graphene side gates are fabricated by a single step of electron beam lithography and an O2 etching procedure. A comparative study of the electrical transport properties as a function of a bias applied to the side and back gate is conducted. The side gates allow for a much more efficient modulation of the charge density in the graphene channel owing to the larger maximum electric field which can experimentally be accomplished. Furthermore, the leakage between the side gate and the graphene channel is studied in a vacuum environment. It is found that the transport between graphene and the side gate is associated with Fowler-Nordheim tunnelling and Frenkel-Poole transport. More specifically, for voltages less than 60 V, the Frenkel-Poole transport dominates the transport, whereas the Fowler-Nordheim tunnelling governs the transport at higher bias. Finally, optoelectronic properties of graphene-WS2 heterostructure are explored. An ionic polymer is used as a top gate to enhance the screening of long-lived trap charges. Responsivities as large as 10^6 A/W under illumination with 600 nm wavelength of light are demonstrated at room temperature. The fall and rise time are in the order of milliseconds due to the screening of the traps by the ionic polymer. This study is the first presentation of the transition metal dichalcogenide (TMDC)-graphene hybrid heterostructure with such a high photoresponsivity and fast response times.
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Yang, Tiebin. "Interfacial Engineering of Thin Single-Crystal Lead Halide Perovskites for High-Performance Optoelectronic Devices." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/28205.
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Metal halide perovskites have demonstrated great potential in energy and optoelectronic device applications, due to their excellent optoelectronic properties. Among all the forms of halide perovskites, single crystals have attracted increasing research interest because of their longer carrier diffusion length, larger charge carrier mobility, and superior stability. However, the practical applications for the bulk perovskite crystals have been limited because of their large thickness and the difficulty of integration. In this regard, searching for the approaches to develop the high-quality halide perovskite thin single crystals with integration compatibility is highly desired, which would further improve the performance of the related devices. Moreover, enabling the halide perovskite thin single crystals with tunable thicknesses and sizes can also promote the construction of the single-crystal halide perovskite heterostructures with well-defined interfaces, which would open up a new realm for the perovskite-based electronic or optoelectronic devices.
In this thesis, the main aims are to develop the facile solution-processed methods to grow the high-quality epitaxial halide perovskite thin single crystals or various mixed-dimensional single-crystal heterostructures and probe the effect of interfaces on the material properties and the related device performance. In particular, the interfacial engineering on the epitaxial thin single crystals and the mixed-dimensional lateral heterostructures further enable various electronic and optoelectronic devices with improved performance and stability. Meanwhile, the thesis also provides in-depth insights into the mechanisms of ion migration and ionic diffusion with the related perovskite systems. The involved work projects and the related findings highlight the great potential and feasibility of halide perovskite thin single crystals and heterostructures in widely-ranged electronic and optoelectronic device applications.
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Magnan, François. "Sulphur- & Nitrogen-Containing π-Conjugated Organic Molecules as Potential Semiconductors for Optoelectronic Devices." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36754.
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Organic semiconductors (OSCs), compared to the more traditional silicon, are enticing materials for the fabrication of optoelectronic devices (e.g., transistors, photovoltaic cells, light-emitting diodes) due notably to the lower cost associated with their preparation and purification, as well as their increased solubility in solvents which can accommodate large-scale fabrication. However, a higher degree of molecular disorder typically results in lower performance than silicon and remains an issue to be adressed. As the structure of an OSC is crucial to its performance, understanding the nature of this structure-property relationship is key to further the field of OSCs. In this regard, this thesis explores the optoelectronic properties of different π-conjugated organic frameworks which incorporate sulphur and nitrogen atoms along the rigid conjugated backbone for their desirable impacts on charge mobilities and stability.
After a brief review of both small-molecule OSCs as well as key experimental techniques employed in the course of this work, chapter three covers the synthesis and characterization of dithiatetrazocines (DTTA), electron-deficient sulphur-nitrogen heterocycles, which were functionalized with various (oligo)thienyls pendants. The impact of both the substitution patterns and the degree of conjugation on the optoelectronic and solid-state properties of the ring system was investigated.
The fourth chapter expands on previous work from the Brusso group that focused on extending the 2D conjugation of tetrathienoanthracene. While oligothienyls were previously shown to effectively increase the degree of conjugation, little to no change in device performance were observed, which was ascribed to disorder of the rotatable pendants. Here, rigid thieno[3,2-b]thiophene was used instead to increase both the degree of conjugation while maintaining structural rigidity, as assessed by optical, electrochemical and theoretical studies.
The fifth chapter introduces preliminary work toward expanding the electron-deficient hexaazatrinaphtylene core with thiophene rings. The resulting concentric donor-acceptor structure promotes luminescent behavior with pronounced emission solvatochromism. Optical measurements were performed before and after intramolecular cyclization of the thiophene rings, to study the impact of aromatization on the optoelectronic properties of the system.
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Berliocchi, Marco. "Optoelectronic devices based on organic materials : design, fabrication and characterization." Lille 1, 2003. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2003/50376-2003-329.pdf.
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Au cours de ce travail, nous avons étudié des polymères du type Poly(arylène-éthynylène) synthétisés à l'aide d'un nouveau procédé (Extended One-Pot). Expérimentalement, nous avons étudié les propriétés de conjugaison en utilisant les méthodes de mesure photophysique en solution liquide et sur des films à l'état solide. Les propriétés de transport électronique ont été caractérisées pour les applications dans les dispositifs électroniques. Nous avons ensuite conçu, fabriqué et caractérisé des dispositifs optoélectroniques basés sur des matériaux organiques (diodes électroluminescentes organiques, transistors organiques, inverseurs). En ce qui concerne les diodes électroluminescentes organiques (OLED), nous avons utilisé différentes couches de transport de trous (Pedot/PSS, EPCZ) et différentes couches actives (thienylene-phenylene copolymer, poly(arylene-ethynylene) 7b, MEH-PPV, BEHP-PPV). Les propriétés de transport de 5,10,15,20-tetra-phenyl-phorphyrin (H2-TPP) ont été analysées par mesures I(V,T} dans le domaine de température 50-350 K. Différents métaux ont été utilisés pour étudier l'influence de l'interface metal/matériau organique sur les propriétés de transport. Les couches organiques ont été déposées par spray coating et par organic molecular beam deposition (OMBD). Les résultats obtenus font apparaître un transport ohmique à toutes les températures étudiées pour les films minces déposés par les deux techniques. Deux mécanismes d'injection ont été mis en évidence: émission thermoi͏̈onique au-dessus d'une barrière indépendante du métal pour T > 250 K et effet tunnel à basse température. Par contre, les films épais déposés par spray coating présentent un comportement différent. Le courant d'obscurité en fonction de la tension appliquée augmente linéairement aux faibles champs électriques, indépendamment du métal utilisé comme contact, et présente la même dépendance avec la température que les films plus minces. Pour des tensions élevées, un mécanisme de transport dépendant du champ électrique de façon non-linéaire a été observé. De plus, la contribution de l'effet tunnel au courant augmente avec le travail de sortie du métal. Les évolutions observées ont été analysées sur la base d'un transport limité par l'injection dans des matériaux organiques amorphes semi-conducteurs. Les résistances des états d'interface et des défauts induits par la déposition ont été considérées pour discuter l'application possible du principe d'Anderson pour l'alignement des bandes et pour justifier les résultats obtenus. Pour les transistors organiques en couches minces, nous avons employé différentes géométries pour les contacts de drain et de source de façon à améliorer les courants de sortie et la mobilité. Des molécules de pentacène et de porphyrine ont été utilisées comme couche active. Les contacts de source et drain ont été préparés en Cr/Au par évaporation sous vide et par un procédé photolitografique sur un substrat de Si02. Après la déposition des contacts, nous avons sublimé (sous vide) une couche mince de matériaux organique (environ 30 nm à la vitesse de 0,2/0,1 Ä/sec). Les mesures du courant de sortie quasi statique et la caractéristique du transfert ont été effectuées dans l'air et sous vide à l'aide d'un Agilent 4155C Semiconductor Parameter Analyzer. L'analyse morphologique de la couche active, par microscopie à force atomique (AFM), a montré une forte corréiation entre la taille des grains de pentacène et les performances des dispositifs. Enfin, nous avons réalisé et caractérisé un inverseur organique avec différentes configurations de transistor de charge. Les nanotubes de carbone mono paroi (Single Wall Carbon Nanotubes - SWCN) ont des propriétés chimiques, mécaniques et électriques fascinantes, très différentes de celles des autres matériaux basés sur le carbone. Les propriétés uniques des SWCN leurs donnent un grand potentiel d'applications: dispositifs nanoélectroniques, stockage de gaz, dispositifs à émission de champ, capteurs et stockage d'énergie. Nous présentons les caractéristiques I-V dans l'air et sous vide (10'2mbar)de différents types de systèmes de SWCN conçus pour des applications technologiques avancées. Nous avons étudié tablettes, fibres formées par des agrégats de SWCN et par dépôt de SWCN sur substrat de verre avec des électrodes coplanaires interdigitées couvertes par une membrane de Nafion® (Nafion 117 Solution Dupont, by Fluka). Le Nafion est une Proton Exchange Membrane et le system nanotubes/Nafion a été choisi en vue des applications possibles sur celles spécialisé pour le carburant.
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Do, Thu Trang. "Electron deficient solution processable organic semiconductors for optoelectronic devices." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/127140/2/Thu_Trang_Do_Thesis.pdf.
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This research is a study of novel developed electron deficient semiconducting materials for optoelectronic devices. It investigates the molecular engineering aspects of new conjugated small molecular electron acceptors with desirable properties such as strong and broad absorption, high electron mobility, and suitable energy levels and good solubility for organic solar cell and organic thin film transistor applications. Furthermore the effect of alkyl chain length on solubility, thermal, optical, electrochemical properties, and device efficiencies is also studied.
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Brombosz, Scott M. "Alkynylated acenothiadiazoles and N-heteroacenes: synthesis, functionalization, and study of the optical properties for optoelectronic and sensory materials." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37102.
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For organic electronic device applications materials are needed which display good charge carrier mobility, good processability, and stability towards oxygen and moisture. Alkynylated N-Heteroacenes fulfill many of these requirements. Substitution with alkyne groups as well as the introduction of the pyrazine subunit both inhibits oxidative degradation at sensitive position in the molecules. Additionally the trialkylsilylethynyl group aides in directing the packing motif as well as vastly increases the solubility over unsubstituted analogues.
A requisite precursor in the synthesis of alkynylated N-heteroacenes is alkynylated acenothiadiazoles. These thiadiazoles display interesting photophysical properties and can be functionalized to produce a wide range of properties in closely related materials. The acenothiadiazoles themselves have potential applications as an N-type semiconductor. Optical gaps and calculated HOMO-LUMO gaps show that these molecules, when compared to known N-type materials, should be easily injected with electrons. Additionally the crystal packing of these compounds shows favorable π-orbital overlap which should provide excellent charge carrier mobilities.
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Lee, Kyoung-Keun. "Implementation of AlGaN/GaN based high electron mobility transistor on ferroelectric materials for multifunctional optoelectronic-acoustic-electronic applications." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28209.
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Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.Committee Chair: William. Alan Doolittle; Committee Member: Jeffrey Nause; Committee Member: Linda S. Milor; Committee Member: Shyh-Chiang Shen; Committee Member: Stephen E. Ralph.
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Goes, Marcos Augusto de. "Desenvolvimento de receptor optico integrado em tecnologia HBT." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/261776.
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Orientador: Jacobus Willibrordus SwartDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
Made available in DSpace on 2018-08-05T07:19:34Z (GMT). No. of bitstreams: 1 Goes_MarcosAugustode_M.pdf: 31444750 bytes, checksum: e7c5cce48b9c9ec73f1804fee26b6062 (MD5) Previous issue date: 2005
Resumo: Esta dissertação de mestrado descreve o estudo, projeto e implementação de um receptor optoeletrônico integrado (OEIC) utilizando a tecnologia de transistores bipolares de heterojunção (HBT), fabricados a partir do material semicondutor arseneto de gálio. A grande vantagem deste transistor é o seu alto ganho e baixa resistência de base, o qual possibilita operações na faixa de gigahertz. A integração do estágio de fotodetecção, feita por um fotodiodo do tipo PIN, com o circuito de amplificação em um mesmo circuito integrado é possível, pois o fotodetector é construído com as camadas de base, coletor e subcoletor do transistor HBT. Com isso, as resistências, capacitâncias e indutâncias parasitas presentes na conexão entre estes dois estágios são minimizadas. Isto permite aos receptores monolíticos trabalharem em freqüências mais altas em relação aos receptores híbridos. O circuito fabricado opera com fontes de luz no comprimento de onda de 850 nm e pode ser utilizado em redes locais de curta distância (LAN)
Abstract: This master degree dissertation describes the study, project and implementation of an optoelectronic integrated circuit (OEIC) using the heterojunction bipolar transistors (HBT) technology over a gallium arsenide substrate. The major advantage of this transistor is its high gain and low base resistance, allowing operation at frequencies in the range of gigahertz. The integration of the photodetection stage, performed by a PIN photodetector, with the amplifier circuit in a single chip is possible because the photodetector is built from the base, collector and subcollector layers of the HBT transistor. Thus, the parasitic resistances, capacitances and inductances between the connection of these two stages are minimized. In this way, monolithic receivers can operate at higher frequencies than hybrid receivers. The fabricated circuit is intended to work with 850 nm light sources and can be used in local area networks (LAN)
Mestrado
Eletrônica, Microeletrônica e Optoeletrônica
Mestre em Engenharia Elétrica
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ROONEY, MILES. "Self-assembled, nanostructured organic materials for applications in electronics and optoelectronic devices." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2018. http://hdl.handle.net/10281/199099.
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l'indagine di due metodi per il controllo molecolare della nano-morfologia di dispositivi opto-elettronici. In primo luogo, un metodo di fotoreticolazione per la creazione di strati semiconduttori insolubili adatti per dispositivi fotovoltaici organici. Una grande serie di semiconduttori squaraine sono studiati in un dispositivo di eterogiunzione di massa. Questo approccio è esteso a nuclei semiconduttori di dichetopirrolopirrolo e naftalene diimmide. Lo studio dettagliato della struttura del film dei materiali viene effettuato.
Il secondo approccio è un'indagine sull'applicabilità dei pigmenti latenti per l'optoelettronica organica. Una serie di fotovoltaici organici sono prodotti in architetture di eterogiunzione planare a doppio strato. I dispositivi a film sottile sono testati con una varietà di interstrati e parametri di elaborazione. Il controllo della nanostruttura di questi dispositivi a film sottile viene esaminato con studi a raggi X. Incorporazione di riflettività a raggi X, raggi X speculari, raggi X a gradiente e studi a raggi x grandangolari. In questo modo la massa e le interfacce dei dispositivi a film sottile possono essere esaminate e caratterizzate. L'approccio del pigmento latente viene applicato anche al campo dei transistor ad effetto di campo organico come lo strato semiconduttore attivo. La natura resistente ai solventi di un pigmento semiconduttore genitore mostra un vantaggio sostanziale per la fabbricazione di tali dispositivi. L'esclusivo riarrangiamento cristallino che si verifica dopo la deprotezione di un pigmento latente determina un miglioramento della mobilità del portatore di carica fino a tre ordini di grandezza mentre estende le possibilità di elaborazione delle successive fasi di deposizione necessarie per completare un transistor ad effetto di campo organico
Queste due tecniche sono sviluppate pensando alla compatibilità industriale. Come tale, viene esplorato un nuovo metodo sintetico per una produzione facile, economica ed ecocompatibile di semiconduttori organici. Un ambiente di reazione micellare viene creato attraverso l'uso del comune tensioattivo e dell'eccipiente di droga Kolliphor EL. L'esclusivo nucleo privo di ossigeno di questo tensioattivo offre un nuovo ambiente per l'esecuzione di comuni reazioni di accoppiamento incrociato quali reazioni Suzuki-Miyaura, Stille e Heck in aria e acqua a temperatura ambiente. Alte rese di oltre il 90% vengono recuperate per nuclei semiconduttori organici complessi. La versatilità di questo approccio è estesa dall'uso del toluene come co-solvente. Questo sistema di co-solvente porta allo sviluppo di un'emulsione che può essere utilizzata per eseguire analisi chimiche complesse. La chimica dell'emulsione offre un modo unico per la sintesi di semiconduttori organici complessi con basso carico di catalizzatore metallico ad alto rendimento.the investigation of two methods for molecular control of the nano-morphology of opto-electronic devices. Firstly, a photocrosslinking method for creating insoluble semiconductor layers suitable for organic photovoltaic devices. A large series of squaraine based semiconductors are investigated in a bulk heterojunction device. This approach is extended to diketopyrrolopyrrole and naphthalene diimide semiconducting cores. Detailed study of the materials film structure is carried out. The second approach is an investigation of the applicability of latent pigments for organic opto-electronics. A series of organic photovoltaics are produced in planar bilayer and bulk heterojunction architectures. The thin film devices are tested with a variety of interlayers and processing parameters. The control of the nanostructure of these thin film devices is examined with X-ray studies. Incorporating X-ray reflectivity, Specular x-ray, Gradient temperature X-ray and grazing wide angle x-ray studies. In this manner the bulk and interfaces of thin film devices can be examined and characterised. The latent pigment approach is also applied to the field of organic field effect transistors as the active semiconducting layer. The solvent resistant nature of a parent semiconducting pigment shows a substantial benefit to the fabrication of such devices. The unique crystalline rearrangement which occurs upon deprotection of a latent pigment results in an improvement in charge carrier mobility of up to three orders of magnitude while extending the processing possibilities of the subsequent deposition steps required to complete an organic field effect transistor These two techniques are developed with the thoughts of industrial compatibility in mind. As such, a novel synthetic method for facile, cheap, and environmentally friendly production of organic semiconductors is explored. A micellar reaction environment is created through the use of the common surfactant and drug excipient Kolliphor EL. The unique oxygen free core of this surfactant offers a new environment for carrying out common cross coupling reactions such as Suzuki-Miyaura, Stille and Heck reactions in air and water at ambient temperature. High Yields of over 90% are recovered for complex organic semiconducting cores. The versatility of this approach is extended by the use of toluene as a co-solvent. This co-solvent system results in the development of an emulsion which can be used to perform complex chemistries. Emulsion chemistry offers a unique way to synthesis complex organic semiconductors with low metallic catalyst loading at high yield.
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Hallani, Rawad Kamal. "Designing Anthradithiophene Derivatives Suitable For Applications in Organic Electronics and Optoelectronics." UKnowledge, 2015. http://uknowledge.uky.edu/chemistry_etds/61.
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Anthradithiophene (ADT) derivatives have proven to be a front-runner in the world of small molecule semiconductors for organic electronics and optoelectronics. This is mainly due to the improved stability, easy tuning of chemical and physical properties, and impressive device performance that these molecules possess, especially in organic field effect transistors (OFET) and organic photovoltaics (OPV). The second chapter of this dissertation shows that reducing the amount of alkylsilylethynyl groups, used for functionalizing and solubilizing the ADT backbone, does alter the chemical, physical and crystallographic properties of ADTs. These changes offer the opportunity to study and observe different intermolecular interactions as well as monitoring their influence on sulfur scrambling in solid state. Additionally, from the early days ADTs and functionalized ADTs have been synthesized as isomeric mixtures. In chapter three, I demonstrate a new and simple method that can separate the syn and anti isomers of the F-TES-ADT and F-TEG-ADT chromatographically. The effects of isomeric purity on crystal packing and field effect transistor performance were studied extensively.
Chapter four of this dissertation reveals a new generation of acceptor (electron poor) ADT derivatives obtained by attaching cyanide as electron withdrawing group (EWG) to the ADT chromophore. An extensive study was conducted on CN-ADT (acceptor) molecules in small molecule (F-TES-ADT) donor/ small molecule (CN-ADT) acceptor binary BHJ blends as well as P3HT/CN-ADT/PCBM ternary BHJ blends. Photophysical studies of the Donor/ acceptor blends (interface, domains, and crystal orientation) were conducted to obtain a better understanding of the film morphology and its effect on solar cell performance.
Finally, the last part of the dissertation, Chapter five, focus on studying singlet fission in ADT derivatives, as well as the effect of varying the size of the alkylsilylethynyl functional group (used for solubilizing the ADT backbone) on altering the electronic couplings and how can that potentially affect the singlet fission rate in these molecules. We also tried to inspect the extent of the correlation between long-range order in crystal packing and singlet fission by monitoring singlet fission rate and efficiency for ADT derivatives with different thin film morphologies.
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Benvenuti, Emilia <1987>. "Organic Light-Emitting Transistor as an Effective Photonic Device Platform: System Engineering for Tuning the Optoelectronic Performance." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/8083/1/Benvenuti_Emilia_tesi.pdf.
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The increasing interest in organic electronics is connected with the easy processability and the possibility of molecular tailoring of the organic semiconductor materials. Ranging from dry deposition techniques in high vacuum to wet processes and nanopatterting techniques, small molecule and polymeric π-conjugated materials have been implemented in a plethora of optoelectronic device applications. Among the other, Organic Light-Emitting Transistors (OLETs) are emerging as an innovative class of multifunctional devices able to integrate the electronic properties of a transistor and the light generation capability. In this thesis, we aim at investigating the photonic and optoelectronic performance of suitable-engineered devices based on different field-effect transistors architecture. Both the active layer and the gate dielectric layer of the device were investigated in order to increase the device performance in terms of brightness, color coordinate and external quantum efficiency. Starting from the study of the active layer in an ambipolar single-layer OLET, we succeeded in controlling the solid-state phases of the oligothiophene derivative namely NT4N. By means of three different deposition techniques (thermal sublimation, supersonic molecular beam deposition, lithographically controlled wetting) we investigated the influence of the different molecular packing motifs on the field-effect charge mobility. Given the limited number of efficient electroluminescent organic small molecules with high field-effect charge mobility, we adopted another approach for enhancing the figures of merit of OLET devices by implementing a multilayer heterostructure comprised by a charge-transport layer and a light-emitting layer. By introducing a newly-synthetized anthracene-based twisted oligomer as emissive layer a deep blue emitting unipolar OLET was realized. Finally, the integration of a high-capacitance hybrid photonic crystal as gate dielectric into the single-layer ambipolar OLET based on NT4N permitted to achieve low gate threshold voltages, and consequently intense brightness, together with modulation of the spectral and spatial characteristics of the emitted electroluminescence.
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Baek, Eunhye [Verfasser], Gianaurelio [Gutachter] Cuniberti, and Ronald [Gutachter] Tetzlaff. "Multi-functional Hybrid Gating Silicon Nanowire Field-effect Transistors : From Optoelectronics to Neuromorphic Application / Eunhye Baek ; Gutachter: Gianaurelio Cuniberti, Ronald Tetzlaff." Dresden : Technische Universität Dresden, 2020. http://d-nb.info/1227202164/34.
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Liao, Si-yu. "Caractérisation électrique et électro-optique de transistor à base de nanotube de carbone en vue de leur modélisation compacte." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14254/document.
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Afin de permettre de développer un modèle de mémoire non-volatile basée sur le transistor à nanotube de carbone à commande optique qui est utilisée dans des circuits électroniques neuromorphiques, il est nécessaire de comprendre les physiques électroniques et optoélectroniques des nanotubes de carbone, en particulier l’origine de l'effet mémoire que présente ces transistors. C’est dans ce contexte général que cette thèse s'intègre. Le travail est mené sur trois plans :• Caractériser électriquement et optoélectroniquement des structures de test des CNTFETs et des OG-CNTFETs.• Développer un modèle compact pour les contacts Schottky dans les transistors à nanotube de carbone de la façon auto-cohérente basé sur le diamètre et la nature du métal d’électrode en utilisant la méthode de la barrière effective avec les paramètres nécessaires calibrés.• Modéliser l'OG-CNTFET selon les régimes de fonctionnement, lecture, écriture, effacement ou programmation pour application à une mémoire non-volatile en intégrant le mécanisme de piégeage et dépiégeage à l’interface polymère/oxydeThis PhD thesis presents a computationally efficient physics-based compact model for optically-gated carbon nanotube field effect transistors (OG-CNTFETs), especially in the non-volatile memory application. This model includes memory operations such as “read”, “write”, “erase” or “program”, and “reset” which are modeled using trapping and detrapping mechanisms at the polymer/oxide interface. The relaxation of the memory state is taken into account. Furthermore, the self-consistent modeling of Schottky barriers at contacts between the carbon nanotube channel and metal electrodes is integrated in this model applying the effective Schottky barrier method. The Schottky contact model can be included in CNTFET based devices for a typical biasing range of carbon nanotube transistors. This compact model is validated by the good agreement between simulation results and experimental data (I-V characteristics). In the non-volatile memory application, this model can fully reproduce device behaviors in transient simulations. A prediction study of the key technological parameter, the CNT diameter variety is established to expect its impact on the transistor performance, and more importantly, on the memory operation. In the other hand, this thesis presents a preliminary electric characterization (I-V) of CNTFETs and OG-CNTFETs for the device modeling database. A preliminary optoelectronic characterization method is proposed
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Fallahi, Mahmoud. "Intégration hétérogène d'un détecteur N-CdTe à un transistor à effet de champ GaAlAs/GaAs." Toulouse 3, 1988. http://www.theses.fr/1988TOU30188.
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On realise sur un meme substrat gaas semi isolant des dispositifs comportant un photoconducteur interdigite cdte et un transistor fet gaalas/gaas pour montrer la faisabilite des circuits heterogenes. On developpe un modele de simulation pour concevoir les masques et analyser les caracteristiques du circuit. Pour realiser le transistor, on utilise la technique d'epitaxie en phase liquide. La croissance de la couche detectrice est obtenue par la methode de transport en phase vapeur a courte distance. On montre la compatibilite thermique et technologique de l'integration. Presentation, etude et caracterisation des dispositifs realises
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Chen, Yani. "Dispositifs hybrides à base de carbone : fonctionnalisation de nanotubes et de graphène avec des molécules actives." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY025/document.
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Dans le cadre de la recherche sur les dispositifs post-CMOS, l'électronique moléculaire bénéficie de la polyvalence de la chimie organique,qui offre de nouvelles fonctions alliant spécificités optiques et électroniques, tout en accédant au régime de confinement quantique intrinsèque aux petites molécules. Conducteurs 1D, les nanotubes de carbone font le lien entre l’électronique des petites molécules émergente et la technologie des semi-conducteurs, tout en tirant parti de la chimie organique. Au-delà de la miniaturisation, ils offrent la possibilité de concevoir de nouveaux dispositifs pour des capteurs, l’optoélectronique et l’électronique quantique. Cependant, la plupart des études se concentrent sur leurs applications aux capteurs ou pour le photovoltaïque qui impliquent un ensemble macroscopique de nanotubes. Dans ce cas, les transferts d'excitation sont moyennés sur un ensemble statistique, ce qui empêche l'accès à leurs mécanismes fondamentaux. Il est donc nécessaire de concevoir des dispositifs fonctionnels à base de nanotubes de carbone individuels. Pour cela, les nanotubes double paroi ont de nombreux avantages sur les monoparois. En général, ils présentent une stabilité plus élevée, qui peut être d’une aide substantielle dans des expériences à haute intensité et à fort champ. Ils réalisent un système cœur-coquille: leur structure concentrique suggère leur utilisation pour réaliser indépendamment un dopage ou une fonctionnalisation des tubes intérieur et extérieur.Dans ce projet de thèse, nous étudions des transistors à effet de champ basés sur des systèmes hybrides nanotubes individuels double paroi / chromophore.Nous présentons d'abord le procédé de fabrication de transistors à effet de champ de nanotubes de carbone à paroi individuels (DWFET), qui sont ensuite caractérisés à la fois par des techniques optiques et électriques. Nous avons notamment étudié le couplage électron-phonon par spectroscopie Raman sous dopage électrostatique. Le tube métallique interne apparaît également affecté par la grille électrostatique et montre des changements significatifs de la signature Raman.Nous avons ensuite fonctionnalisé les DWFETde façon non covalente avec deux types de molécules optiquement sensibles (terpyridine d'osmium et complexe de zinc (II) métalloporphyrine). Les hybrides sont caractérisés à la fois en optique et en transport électronique. Il apparaît un transfert de charge entre les molécules et le DWNT qui joue le rôle d’une grille chimique détectable par spectroscopie Raman et transport électrique, ce qui indique que les DWFET peuvent être utilisés pour la détection de molécules. L'excitation lumineuse des molécules conduit à un dopage des hybrides et permet de plus de révéler le couplage entre les parois des nanotubes.De plus, nous avons réalisé des expériences de grille optique à longueur d'onde variable sur les dispositifs hybrides, couplant à la fois la spectroscopie Raman et des mesures de transport électrique de la température ambiante jusqu’à la température de l'hélium. Le contrôle optique du comportement électronique des hybrides est expliqué en termes de transfert de charge photo-induit entre les molécules greffées et le DWNT. Par conséquent, nos FET hybrides peuvent être utilisés comme mémoire à commande optique jusqu’au régime de transfert d'électrons uniquesIn the frame of the intense research on electronics beyond CMOS, molecular electronics offers the versatility of organic chemistry in order to tailor new functions combining optical and electronic specifications, while accessing the quantum confined regime intrinsic to small molecules. As 1D conductors, carbon nanotubes bridge the gap between small molecules electronics and semiconductor technology with great promises while being a playground for organic chemistry. Beyond miniaturization, they offer the opportunity to design new devices from accurate sensors to optoelectronic and quantum devices. However most studies focus on sensor or photovoltaic applications and thus involve a macroscopic assembly of nanotubes. This averages the excitation transfers, which prevents access to their fundamental mechanisms. This requires the design of individual carbon nanotube based functional devices. For this issue double wall carbon nanotubes have many advantages over simple SWNTs. In general, they exhibit higher stability, which can be a substantial help in high-current and high-field experiments. They realize a core-shell system: their concentric structure suggests its use for independent doping or functionalization of inner and outer tubes.In this PhD project, we demonstrate field effect transistors based on hybrid systems of individual double wall carbon nanotubes and optically sensitive molecule.We first introduce the method for making individual double wall carbon nanotube field effect transistors (DWNT FETs), which are then characterized both optically and electrically. We also studied the electron phonon coupling in the DWNT system by Raman spectroscopy with electrostatic gating. The inner metallic tube is also affected by the electrostatic gate and shows dramatic changes of the overall Raman signature.We then functionalized non covalently two kinds of optically sensitive molecules to DWNT and graphene FETs (Terpyridine Osmium complex and Zinc(II) metalloporphyrin). The hybrids are characterized both optically and electrically. Charge transfer between DWNTs and molecules plays as a chemical gating which can be detected by Raman spectroscopy as well as electrical transport measurements, which indicates that the DWNT FETs can be utilized for molecular sensing. Light excitation of the molecules leads to doping of the hybrids and reveals the coupling between the nanotube walls.Moreover, we realized wavelength dependent optical gating on the hybrid device, detected by both Raman spectroscopy and electrical transport measurements at both room temperature and helium temperature. The optical control of the hybrids’ electronic behavior will be elucidated in terms of photo-induced charge transfer between the grafted molecules and the DWNT component. As a consequence, this hybrid FETs can be used as an optically controlled memory down to single electron transfers at low temperature
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Mogniotte, Jean-François. "Conception d'un circuit intégré en SiC appliqué aux convertisseur de moyenne puissance." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0004/document.
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L’émergence d’interrupteurs de puissance en SiC permet d’envisager des convertisseurs de puissance capables de fonctionner au sein des environnements sévères tels que la haute tension (> 10 kV ) et la haute température (> 300 °C). Aucune solution de commande spécifique à ces environnements n’existe pour le moment. Le développement de fonctions élémentaires en SiC (comparateur, oscillateur) est une étape préliminaire à la réalisation d’un premier démonstrateur. Plusieurs laboratoires ont développé des fonctions basées sur des transistors bipolaires, MOSFETs ou JFETs. Cependant les recherches ont principalement portées sur la conception de fonctions logiques et non sur l’intégration de drivers de puissance. Le laboratoire AMPERE (INSA de Lyon) et le Centre National de Microélectronique de Barcelone (Espagne) ont conçu un MESFET latéral double grille en SiC. Ce composant élémentaire sera à la base des différentes fonctions intégrées envisagées. L’objectif de ces recherches est la réalisation d’un convertisseur élévateur de tension "boost" monolithique et de sa commande en SiC. La démarche scientifique a consisté à définir dans un premier temps un modèle de simulation SPICE du MESFET SiC à partir de caractérisations électriques statique et dynamique. En se basant sur ce modèle, des circuits analogiques tels que des amplificateurs, oscillateurs, paires différentielles, trigger de Schmitt ont été conçus pour élaborer le circuit de commande (driver). La conception de ces fonctions s’avère complexe puisqu’il n’existe pas de MESFETs de type P et une polarisation négative de -15 V est nécessaire au blocage des MESFETs SiC. Une structure constituée d’un pont redresseur, d’un boost régulé avec sa commande basée sur ces différentes fonctions a été réalisée et simulée sous SPICE. L’ensemble de cette structure a été fabriqué au CNM de Barcelone sur un même substrat SiC semi-isolant. L’intégration des éléments passifs n’a pas été envisagée de façon monolithique (mais pourrait être considérée pour les inductances et capacités dans la mesure où les valeurs des composants intégrés sont compatibles avec les processus de réalisation). Le convertisseur a été dimensionné pour délivrer une de puissance de 2.2 W pour une surface de 0.27 cm2, soit 8.14 W/cm2. Les caractérisations électriques des différents composants latéraux (résistances, diodes, transistors) valident la conception, le dimensionnement et le procédé de fabrication de ces structures élémentaires, mais aussi de la majorité des fonctions analogiques. Les résultats obtenus permettent d’envisager la réalisation d’un driver monolithique de composants Grand Gap. La perspective des travaux porte désormais sur la réalisation complète du démonstrateur et sur l’étude de son comportement en environnement sévère notamment en haute température (> 300 °C). Des analyses des mécanismes de dégradation et de fiabilité des convertisseurs intégrés devront alors être envisagéesThe new SiC power switches is able to consider power converters, which could operate in harsh environments as in High Voltage (> 10kV) and High Temperature (> 300 °C). Currently, they are no specific solutions for controlling these devices in harsh environments. The development of elementary functions in SiC is a preliminary step toward the realization of a first demonstrator for these fields of applications. AMPERE laboratory (France) and the National Center of Microelectronic of Barcelona (Spain) have elaborated an elementary electrical compound, which is a lateral dual gate MESFET in Silicon Carbide (SiC). The purpose of this research is to conceive a monolithic power converter and its driver in SiC. The scientific approach has consisted of defining in a first time a SPICE model of the elementary MESFET from electric characterizations (fitting). Analog functions as : comparator, ring oscillator, Schmitt’s trigger . . . have been designed thanks to this SPICE’s model. A device based on a bridge rectifier, a regulated "boost" and its driver has been established and simulated with the SPICE Simulator. The converter has been sized for supplying 2.2 W for an area of 0.27 cm2. This device has been fabricated at CNM of Barcelona on semi-insulating SiC substrate. The electrical characterizations of the lateral compounds (resistors, diodes, MESFETs) checked the design, the "sizing" and the manufacturing process of these elementary devices and analog functions. The experimental results is able to considerer a monolithic driver in Wide Band Gap. The prospects of this research is now to realize a fully integrated power converter in SiC and study its behavior in harsh environments (especially in high temperature > 300 °C). Analysis of degradation mechanisms and reliability of the power converters would be so considerer in the future
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Chang, Chia-Hung, and 張家弘. "The optoelectronic characteristics on the InP nanowire field-effect transistors." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/85364552939487000047.
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碩士國立交通大學
電子物理系所
97
Indium phosphide (InP) nanowires with an average diameter of 20 nm were grown for the fabrication of two-probe devices by using the standard electron-beam lithography technique. Current-voltage (I-V) behaviors of the nanowire devices were measured at temperatures from 300℃ down to 120℃. The resistance of the nanowire devices increases with decreasing temperatures, implying the semiconducting behavior in the nanowires. The electron transport as well as the temperature dependent resistance R(T) was calculated. We found that, for the devices having low room-temperature resistance, the R(T) agrees well with the thermal activated transport theory. The low resistance devices might give the intrinsic electrical poperties of the InP nanowires. On the other hand, the high resistance devices could be used to study the electrical properties from the nanocontact. Additionally, the back gate technique was adopted to check the field-effect properties. Electrical characterization on the InP nanowire field-effect transistors indicates that the InP nanowires are natively n-type semiconductors. Moreover, the optoelectronic properties of the two-probe nanowire devices were explored under the exposure of the green light laser (532 nm). We found that the photocurrent, in comparison with the dark current, enhances with a ratio up to 100% for the contact dominated devices while the excited photocurrent is still smaller than that in the nanowire dominated devices.
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Peng, Tien-Hsin, and 彭天欣. "Studies on the Optoelectronic Properties of WSe2 Thin Film Transistors." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/93tyk8.
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碩士國立臺灣大學
電子工程學研究所
107
In this study, high-performance multilayer WSe2 filed-effect transistors were demonstrated by rapid thermal annealing process in oxygen ambient. The experimental results indicate that the field-effect mobility of hole could be enhanced from 1.49 to 31.1 cm^2/Vs after oxygen annealing treatment. The on/off-current ratio will up to so high as 10^7. It’s also used 2D-layered hexagonal-boron nitride (h-BN) as substrate or passivation layer to observe the absorbed oxygen on the channel. Additionally, it confirmed the existence of oxygen and p-doping effect after annealing treatment by measuring Raman spectra and XPS. According to the above results, both oxygen molecules on the top and at the bottom of the channel have the dramatic influence on the WSe2 TFTs’ performance, and, moreover, this work provides a method to improve the device performance of WSe2 TFTs and change the undesirable ambipolar transport to the unipolar, which is essential to the implementation of CMOS logic. Moreover, the WSe2 homostructure rectifying diode is demonstrated, p-type and n-type WSe2 regions were formed by adopting different layer WSe2 thicknesses. Typically, the common way to fabricate two-dimensional material based diode is to use heterostructure by stacking two different carrier type and band gap energies materials. However, there is always lattice mismatch at the junction, leading to the degraded photoresponse of the diodes. In order to reduce the problems of heterostructure diode, layer thickness dependent band gap energy of WSe2 is reported and applied to fabricate homostructure diode. The ideality factor of the current-voltage characteristic is 1.64 and the current rectification ratio can reach to 10^3. The optical properties of the diode, including fill factor 45.7%, responsivity 16.02 mA/W and EQE 3.06% are reported. It is concluded that the WSe2 homojunction diode can be applied in photodetectors, switches, solar cells etc.
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Chen, Jing-Yuh, and 陳敬育. "Investigation of InP-based Heterojunction Bipolar Transistors and Optoelectronic Switching Devices." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/04342709273737323496.
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博士國立成功大學
微電子工程研究所碩博士班
93
In this dissertation, we have successfully fabricated and demonstrated InP-based heterojunction bipolar transistors (HBTs). The characteristics of InP/InGaAs HBT with a superlattice-collector (SC) structure and InGaAs/InGaAsP composite-collector HBT (CCHBT) are measured and discussed. In addition, two interesting optoelectric switches, a double-barrier-emitter triangular-barrier optoelectronic switch (DTOS) and a bulk-barrier optoelectronic switch (BBOS) with an AlGaAs/δ(n+)-doped sheet/GaAs/InAlGaP collector structure are also investigated and discussed. The studied devices were grown by low-pressure metal organic chemical vapor deposition (LP-MOCVD) and molecular beam epitaxy (MBE). The characteristics of epitaxial layers will be analyzed by double-crystal x-ray diffraction (DCXRD), photoluminescence (PL), and electrochemical CV profiling (ECV). After finishing the growth, mesa-type devices were formed by utilizing photolithography, vacuum evaporation, lift-off, alloying and selective etching techniques. DC characteristics of an interesting InP/InGaAs heterojunction bipolar transistor with a superlattice (SL) structure incorporated in the base-collector (B-C) junction are demonstrated. In the SL structure, holes injected from the collector collide with holes confined in the SL and impact them out of the SL across the valence-band discontinuities. With a collector-emitter (C-E) voltage VCE less than the C-E breakdown voltage BVCEO, the current gain can be increased at base-current inputs because the released holes from the SL inject into the base to cause the E-B junction operating under more forward-biased condition. An AC current gain up to 204 is obtained. At B-E voltage VBE inputs, the released holes travel to the base terminal to decrease the base current. The studied HBT exhibits common-emitter current gains exceeding 47 at low current levels and useful gains spreading over 7 orders of magnitude of collector current. DC characteristics of an interesting HBT with an InGaAs/InGaAsP composite-collector (CC) structure are studied and reported. Due to the insertion of an InGaAsP setback layer at the base-emitter (B-E) heterojunction, the potential spikes as well as the electron blocking effect are suppressed significantly. In addition, the presence of an effective base-collector (B-C) homojunction can substantially reduce the current blocking effect. The studied device gives impressed dc performance including small offset and saturation voltages without degrading the breakdown behaviors. The typical dc current gain of 118 and the desired current amplification over 11 decades of magnitude of collector current IC are obtained. On the other hand, a triangular-barrier and a double-barrier structure are combined to form a double-barrier-emitter triangular-barrier optoelectronic switch (DTOS). In the structure center of the triangular barrier, a p-type delta-doped quantum well is inserted to enhance the hole confinement. Owing to the resonant tunneling through the double-barrier structure and avalanche multiplication in the reverse-biased junction, N-shaped and S-shaped negative-differential-resistance (NDR) phenomena occur in the current-voltage (I-V) characteristics under normal and reverse operation modes, respectively. The NDR characteristics show variations from dark to illumination condition. Temperature effects on the NDRs of the DTOS are also obvious. The illumination and temperature influences on the device characteristics are investigated. Two-terminal switching performances are observed in a new bulk-barrier optoelectronic switch (BBOS) with an AlGaAs/δ(n+)/GaAs/InAlGaP collector structure. The device shows that the switching action takes place from a low current state to a high current state through a region of NDR. The transition from either state to the other may be induced by an appropriate optical or electrical input. It is seen that the effect of illumination increases the switching voltage VS, holding voltage VH, holding current IH and decreases the switching current IS, which is quite different from other reported results. In addition, it possesses obvious NDR even up to 435K. This high-temperature performance provides the studied device with potential high-temperature applications.
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Tsung-HanYang and 楊宗翰. "Investigation of Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistors and Optoelectronic Applications." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/43577182141787656932.
Full textAbstract:
碩士國立成功大學
微電子工程研究所碩博士班
101
In this thesis, amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) with Ga2O3 high k material were fabricated and analysis of deep UV phototransistor investigated. First, we apply a-IGZO thin film as channel layer to the fabrication of TFT with Ga2O3/SiO2 gate dielectric. It was found that the field-effect mobility were 11.2 cm2/Vs, threshold voltage of 0.5 V, subthreshold swing of 0.29 V/decade and Ion/Ioff of 105 for a-IGZO TFT with Ga2O3/SiO2 gate dielectric. Additionally, we report the effect of different silicon oxide thickness on the device performance of a-IGZO TFTs was investigated. In the second part of our experiment, the fabrication of a-IGZO thin-film transistor with a Ga2O3 buffer layer on a glass substrate was demonstrated. The room-temperature-deposited a-IGZO channel with Ga2O3 exhibits threshold voltage of 0.75 V, drain-source current on/off ratio of 1.4×105, subthreshold swing of 0.14 V/decade, and field-effect mobility of 39 cm2/Vs under a low operation voltage. Compared with and without high k Ga2O3 buffer layer, it was found that we can achieve higher mobility, low threshold voltage and operation voltage. These results could be contributed to the Ga2O3 buffer layer decrease interface trap density efficiently. On the part of a-IGZO phototransistor, a deep-UV sensitive a-IGZO phototransistor with Ga2O3 high k material was fabricated. Using Ga2O3 as gate dielectric, it was found that measured current increased from 3.8×10-12 A to 2.3×10-5 A as we illuminated the sample with λ= 250 nm UV light when VG was biased at 0 V. It was found that measured responsivity of the device was 1.7 A/W and we could achieve the photosensitivity of 1.4×104 when the device was biased at 0 V. Then using Ga2O3 as buffer layer, it was found that measured current increased from 1.1×10-10 A to 1.3×10-5 A as we illuminated the sample with λ= 250 nm UV light and the measured responsivity of the device was 1.58 A/W. Beside, with an incident light wavelength of 380 nm, it was found that measured responsivity of the device was 1.7×10-4 A/W and we could achieve the photosensitivity of 1×105. These results suggest that the a-IGZO thin film transistors have the low power consumption, high responsivity and rejection ratio when used in UV detection.
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Chou, Yung-Lin, and 周勇霖. "Investigation of Temperature-Sensing Mechanism and Integrated Optoelectronic System in Light-Emitting Transistors." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/57544419341594992202.
Full textAbstract:
碩士國立臺灣大學
光電工程學研究所
104
In this thesis, we investigate two characteristics of (1) the temperature-sensing effect and (2) the optical-to-electrical signal transmission in light-emitting transistors (LETs). By embedding the quantum well (QW) into the base region of the heterojunction bipolar transistor (HBTs), the HBTs will form the QW-HBTs (or so-called LETs). In the temperature-sensing investigation, we analyze the thermal effects on the electrical signals. Comparing the temperature-dependent current gain, β(T), in QW-HBTs to the current gain of the normal HBTs, we can observe the totally opposite trend, presenting that the QW plays an important role in the thermal mechanism. We derive the modified charge control model and rate equations to analyze the carrier capturing and escaping behavior related to the QW and the carriers coupling to the whole base charge. Moreover, we alter the epitaxial structures and compare the effects on the trend of β(T) through the theoretical model we build and simulation software. We can find out the optimal layer design of current gain curve for applying to the temperature sensing in the future. For the effects on the different device geometries, because of many non-ideal effects, we directly fabricate the QW-HBT devices with different layout designs and variations. Also the simulation tool is used to help the analyses of the thermal effects on the β(T). In the optical-to-electrical signal transmission part, we demonstrate the integration of optoelectronic system realized by the ring-shaped light-emitting transistors, or RLETs. We fabricate the LETs with the ring-shaped resonator structures, and analyze the effects of different sizes and geometries on the optical and electrical outputs. Owing to the whispering gallery modes (WGMs), the optical modes will propagate along the ring periphery without any output direction. In order to communicate to other devices, we incorporate the waveguides to guide the light in the specific direction. In the end of the waveguide, we incorporate the photodetectors which consist of the same epitaxial structure of RLETs. According to Franz-Keldysh effect, the light from the RLETs can be transferred to the electrical signal by the base-collector junction of the detector LETs, and hence we can calculate the responsivity. This thesis presents the functional characteristics of LETs, and we hope to contribute to the development of the optoelectronic integrated circuits (OEICs) in the future.
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Chih-YuWei and 魏志諭. "Investigation of Indium-Gallium-Oxide (In-Ga-O) Thin Film Transistors and Optoelectronic Applications." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/kzm88p.
Full textAbstract:
碩士國立成功大學
微電子工程研究所
103
In this thesis, we use In-Ga-O thin film as active layer to fabricate and investigate thin film transistors and UV phototransistor. Firstly, we deposit and analyze In-Ga-O thin films, and In-Ga-O thin films show amorphous structure and smooth surface. And then we realize In-Ga-O MSM UV photodetectors. It is found that we could change the conductivity and cutoff wavelength of the fabricated photodetectors by changing the RF sputtering power for the In2O3 target. Secondly, we fabricate In-Ga-O TFTs. The performance of the TFTs is found to be strongly dependent on the element composition of channel layer. The optimized device, sample F, exhibites a good electrical property with a μFE of 6.5 cm2/Vs, a SS of 0.33 V/decade, and an on/off current ratio of 5.1×106. The cutoff wavelength of In-Ga-O phototransistors is red-shifted from 270 to 310 nm with increase in indium content. The UV-to-visible rejection ratio and photoresponsivity of the fabricated phototransistors are 4.8×103 and 0.24 A/W in sample F. Lastly, we fabricate dual channel In-Ga-O TFTs. We realize bilayer structure which can be deposited in-situ with same material, and the performance of TFTs can be improved through bandgap engineering. The fabricated device, sample L, exhibites good electrical properties with a μFE of 53.2 cm2/Vs, a SS of 0.19 V/decade, and an on/off current ratio of 3.2×107. Compared with the TFTs with single In-Ga-O layer, the photoresponsivity of dual channel TFTs are enhanced by the bilayer structure. The UV-to-visible rejection ratio and photoresponsivity of the fabricated phototransistors are 103 and 14.26 A/W in sample L. Degradation in UV-to-visible rejection ratio can be attributed to the relative high density of oxygen vacancies in front channel.
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Man-YuChang and 張曼妤. "Fabrication of Indium-Zirconium-Oxide Thin Film Transistors by Co-Sputtering and Optoelectronic Applications." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/84844050773886466704.
Full textAbstract:
碩士國立成功大學
微電子工程研究所
104
In my experiment, I use the both targets of indium oxide and zirconium dioxide to co-sputter to fabricate the In-Zr-O thin film transistors and UV phototransistors. The In-Zr-O thin film is analyzed by X-ray diffraction and atomic force microscope and we found that it is crystalline structure and has smooth surface which are beneficial to enhance the TFTs’ characteristics. And then, the In-Zr-O MSM UV photodetectors with Pt ohmic contact electrodes are realized. It is found that changing the RF sputtering power for indium oxide target will transform the cut off wavelength and conductivity of the photodetectors. Next, it will focus on the investigation of the In-Zr-O thin film transistors. We change the content of In2O3 in the thin film in order to fabricate Sample A to Sample I and it is found that Sample F owns good electrical property with SS of 0.43 (V/decade), μFE of 50.78 (cm2V−1s−1) and Ion/off of 9.98×105. Furthermore, using 250-Watt Xenon lamp to emit 230–500 nm light will modulate the cut off wavelength of the UV phototransistors from 310 nm to 340 nm as the content of In2O3 is rising. The photoresponsivity and UV-to-visible rejection ratio of the phototransistors for Sample F are 1.05 (A/W) and 2.2×104. Finally, we fabricate bilayer In-Zr-O thin film transistors with double channel which is composed of Sample C as front channel and Sample D–F as back channel and we call them Sample J, K and L. Sample L shows better property with SS of 0.33 (V/decade), μFE of 58.16 (cm2V−1s−1) and Ion/off of 3.02×106. Compared with the TFTs with single layer structure, the physical characteristics of the TFTs with bilayer structure is enhanced. The cut off wavelength of the UV phototransistors rises to 325 nm–360 nm and the photoresponsivity and UV-to-visible rejection ratio of Sample L are 1.73 (A/W) and 3.2×102.
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Yang, Man-Chun, and 楊曼君. "Electrical Analysis and Physical Mechanisms of a-InGaZnO Thin Film Transistors for Optoelectronic Application." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/00807195884948914180.
Full textAbstract:
碩士國立中山大學
光電工程學系研究所
101
In recent year, the large size and high pixel is need for variously advanced displays. Thus, the stable reliability and standard characteristic is most important for thin film transistor (TFT). The advantageous features of MOS (Metal oxide-based) TFTs are low temperature of fabrication, higher on/off current ratio, and higher electron mobility (> 10cm2/Vs). However, high mobility reduces power consumption and increase operation frequency. Due to the superior characteristics in amorphous metal oxide TFT, therefore, the amorphous metal oxide TFT is a very promising material for the display application in future. We utilize inverted stagger a-IGZO TFTs with via type device. Although the a-IGZO TFT has many advantages, it is always suffer from the instability of illumination and long term bias stress due to oxygen vacancy and interface trap states. We varied different structure to discuss the mechanism under bias stress or illumination. First, we analyzed degradation of a-IGZO TFTs with fringe field (FF) structures by varying the area of active layer in width direction under high current stress (HCS). The degradation of devices can be attributed to the current-induced Joule heating phenomenon, causing a positive threshold voltage shift. The more voltage shift is associated with reduction of heat dissipation in IGZO with increased area of active layer. The second part is mainly the examination of a-IGZO TFT instability under front light illumination. The structure is varied from the extension of Metal2 (M2) and the light-exposure-length is defined from the source electrode along the length direction. The UV illumination induced electron-hole pair generation, with the subthreshold photo-leakage current resulting from the holes accumulation inducing source-side-barrier-lowering. In third part is varying from overlapped via-contact between gate and source/drain to non-overlapped via-contact (offset length) under UV back light. The on-current is decreased gradually with increasing source-offset length due to the increased uncontrollable offset region in dark. To use this difference of Id-Vg transfer characteristic curve before and after UV illumination, we design the UV sensor and it can be integrated in panel without changing the mask number and extra cost.
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Fiebig, Matthias [Verfasser]. "Spatially resolved electronic and optoelectronic measurements of pentacene thin film transistors / vorgelegt von Matthias Fiebig." 2010. http://d-nb.info/1008352845/34.
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Cheng-HuaWen and 溫承樺. "Investigation of indium zinc oxide thin film transistors fabricated by sputtered system and their optoelectronic application." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/60689307700462474211.
Full textAbstract:
碩士國立成功大學
微電子工程研究所
102
In this thesis, we use RF sputtering system to fabricate a-IZO thin film and vary the oxygen flow to obtain IZO thin films of different electrical characteristics. In terms of electrical device, we first fabricate the TFT applying the a-IZO thin film as active layer and SiO2 as gate dielectric layer. We obtain the optimized TFT having the mobility of 8.71 cm2/Vs, threshold voltage of 0V, subthreshold swing of 0.25 V/decade and Ion/Ioff ratio of 6.8×104. In addition, we find that the devices have different electrical characteristic with different oxygen ratio. And we obtain the optimized IZO thin film under 10% oxygen ratio. In the first part of the experiment, we fabricate the a-IZO thin film transistor using SiO2 as gate dielectric. In second part, we make an improvement on the SiO2 dielectric with SiN buffer layer. The TFT using SiN/SiO2 gate dielectric has the mobility of 13.67 cm2/Vs, threshold voltage of 1.27 V, subthreshold swing of 0.216 V/decade and Ion/Ioff ratio of 1.57E6 . Compared with normal SiO2 dielectric layer, we obtain higher Ion/Ioff ratio after impact SiN improvement. In addition, we also replace SiO2 with high κ material Al2O3 as gate dielectric. The Al2O3 TFT has the mobility of 34.15 cm2/Vs, threshold voltage of 2.51V, subthreshold swing of 0.2 V/decade and Ion/Ioff ratio of 7.36E6. At last, we also investigate the reliability of these dielectric In the part of a-IZO thin film photoelectrical application, we fabricate the IZO MSM photodetector and IZO thin film phototransistor with IZO thin film of 10% oxygen ratio. The photodetector has Ion/Ioff ratio of 7.21E2 and rejection ratio of 325 under 5V bias. The phototransistor has the Ion/Ioff ratio of 2.54E4, rejection ratio of 1.2E6 under -5V bias. The result indicates that the phototransistor has the better photoelectrical characteristic than photodetector. As we know, IZO is easy to form oxygen vacancy, which could yield a leakage current path for IZO device. Therefore, a simple surface treatment process is reported for improving its surface defects. We deposit 3-aminopropyltrimethoxysilane (APTMS) onto the IZO MSM photodetector to passivate its surface. After APTMS modification, the dark current of IZO phtodetector has decrease nearly an order and the rejection ratio increase from 325 to 728.
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Hung-HsuLin and 林泓旭. "Investigation of magnesium zinc oxide thin film transistors fabricated by sputtered system and their optoelectronic application." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/99837492176738674372.
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Wei-TingWu and 吳韋廷. "Investigation of Indium Titanium Zinc Oxide Thin Film Transistors Fabricated by RF Sputtering System and Their Optoelectronic Application." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/y972cf.
Full textAbstract:
碩士國立成功大學
電機工程學系
105
In this thesis, indium titanium zinc oxide (InTiZnO) is deposited by RF magnetron sputtering and the film properties are discussed thoroughly under different processing ambiences. Next, we will use InTiZnO thin film for device fabrication, including photodetectors and thin film transistors (TFTs). In the first part of the experimental results and features discussion, we utilize the RF-sputtering system to grow films with different conditions and the film properties are discussed for three aspects which are structural, optical, and surface/depth element analysis. Thin films are amorphous grown by RF magnetron sputtering. And the measurement results show that the transmittance in the visible region can achieve more than 80%. Next, with the material element analysis, under the different sputtering oxygen flow ratios, films may exhibit different characteristics. The XPS results suggest that as the oxygen flow ratio increases, oxygen defects will decrease. In the second part of the experiment, InTiZnO photodetectors are fabricated under various oxygen flow ratios to investigate differences among these devices. When oxygen flow ratio increases, InTiZnO photodetector can more effectively suppress dark current and the order of magnitude of current reach picoampere level, increasing the on-off ratio of devices. It is found that 4% oxygen flow ratio (Sample B) has the best performance compared to others. And with the optimized fabrication parameters, the dark current is 2.21 × 10−10 A, on-off ratio is 1.29 × 104, and the rejection ratio can reach 4.34 × 103. In the third part, InTiZnO TFTs with silica (SiO2) as the gate dielectric layer are realized. Manipulation of oxygen flow ratios is conducted to find the optimized TFTs. The transfer characteristics of optimized TFTs at room temperature show the field effect mobility of 0.884 cm2/V∙s, threshold voltage of −0.9 V, and subthreshold swing of 0.41 V/dec. The on-off current ratio increased by approximately five orders of magnitude. In addition, we substitute alumina (Al2O3) for silica as the gate dielectric material via atomic layer deposition method. The devices show the field effect mobility of 2.317 cm2/V∙s, threshold voltage of 1.39 V, and subthreshold swing of 0.3 V/dec. The on-off current ratio increased by nearly six orders of magnitude. Lastly, InTiZnO TFTs are operated under light illumination to examine the performance. At no bias, we can obtain a rejection ratio about 1817.
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Jr-WeiLin and 林桎葦. "Tuning the structural and optoelectronic properties of organic/polymeric semiconductors by solvent methods: application to field-effect transistors." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/51702518884527283268.
Full textAbstract:
博士國立成功大學
光電科學與工程研究所
99
Abstract Concerning my investigation in the past 3-and-half years as a candidate for doctor's degree, I would like to write brief summaries by below five paragraphs. Part 1. P3HT The chapter 2 focuses on the microstructural modifications of regioregular poly (3-hexylthiophene) (rr-P3HT) in the small active channel of thin-film transistors (TFTs) during operations. Polarized absorption and microRaman spectroscopy analyses allow us to probe directly the conformation transitions of rr-P3HT chains parallel or perpendicular to the channel by means of exciton bandwidth, interchain electronic coupling, and effective conjugation length. The results of absorption spectra and a joint experimental-theoretical study of Raman spectra show that an external source-to-drain electric field can align rr-P3HT chains parallel to the channel, improving electrical performance after long-term operations, especially charge transport properties. In comparison, the applied external gate field induced an increase in amorphous fraction of the rr-P3HT films. After the analysis, we propose a chain rearrangement model driven by an external electric field to interpret the changes of the effective conjugation length of rr-P3HT, rather than thermal annealing. Our observations provide a thorough explanation for the previously unknown relationships of structure-electronic properties under the extended operations of polymer TFT devices. In chapter 3, combined quasi-swelling and recrystallization concepts, a promising approach was developed to reform distorted segments into the highly-ordered structure with the superlong effective conjugation length (＞ 90mer at least) for polymer chains, which are impressive results compared with those previously reported in the literature. These highly extended polymeric conjugated chains may have important implications for various optoelectronic devices applications and theoretical studies. In chapter 4, we demonstrate high-performance air-stable bottom-contact-top-gate polymer thin-film transistors (TFTs) with linear regime field-effect mobility as high as near 0.2 cm2/Vs using conjugated poly(3-hexylthiophene) (P3HT) as the active layer. A thermal-crosslinked poly(vinylphenol) main layer and a poly(vinylidene fluoride) buffer layer were fabricated on the P3HT layer from the solution process to serve as both the gate dielectric and passivation layer. The ?lin is two orders of magnitude greater than that in bottom-contact-bottom-gate configuration using conventional silicon dioxide gate dielectric. In chapter 5, a series of binary blends of P3HT and insulator polymer, i.e., poly(methyl methacrylate) (PMMA), were prepared and as the active layer of polymeric TFTs. We investigated the correlation of microstructure of the blending films and electrical properties of the TFTs by absorption spectrometer, atomic force microscopy and X-ray diffraction. The result revealed that blending PMMA reduced the crystalline portion of P3HT and produced phase separation morphology of P3HT and PMMA. When appropriate amount of PMMA was added, the devices exhibit better electrical performance that of the device without PMMA. Especially, the optimal TFT with PMMA show enhanced on-current and low-level off-current of only 19 pA. We found that the electrical properties of the P3HT:PMMA blending films-based TFTs could be controlled by adding different concentrations of insulator polymer. Part 2. Pentacene In chapter, a promising and simple method to control the crystal polymorphic transformations of insoluble pentacene through solvent treatments is developed to obtain superior films with stable polymorphs and enhanced intermolecular electronic coupling, as proven by X-ray diffraction, Raman and absorption spectroscopy, and quantum chemical calculations. The degree of polymorphic transformations within films can be managed by the selection of appropriate organic solvents according to the magnitude of pentacene-solvent interaction. A reaction pathway that could interpret how a metastable polymorph T (“thin film” phase) transforms into a more stable polymorph B (“bulk” or “single-crystal” phase) is proposed. The hypothesis is based on the terms of crystal structural parameters, including separation distance, tile angle, and herringbone edge-to-face angle. With the aid of quantum chemical calculations, we combine the binding energy of pentacene dimers and pentacene-solvent interaction energy to develop a new quantitative criterion for the selection of appropriate organic solvents for the structural improvement of organic crystal/films rather than damage. The proposed solvent post-treatments concepts could provide opportunities for improved vacuum-evaporated organic crystal/films and further expand potential applications in organic electronics and photonics.
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Cheng-WeiLin and 林承緯. "Optoelectronic Properties on Indium-Magnesium-Oxide (MIO) Thin Film Transistors and Improvement by Using Cap Layer and Buffer Layer." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/56068341043983267045.
Full textAbstract:
碩士國立成功大學
微電子工程研究所
104
In this thesis, we utilize co-sputter system to prepare amorphous indium magnesium oxide (MIO) thin film; moreover, thin film transistors (TFTs) and UV phototransistors are fabricated and analyzed. First, we deposit a-MIO thin film on the glass substrate and investigate the properties of thin film with adjusting the power of the target. The result of materials analysis show amorphous structure and smooth surface. And then we demonstrate MSM UV photodetectors. It is found that the cutoff wavelength of the phototransistors can shift by changing the RF sputter power of the In2O3 target. With 3 V applied bias, it is found that measured cutoff wavelength are 315 nm, 330 nm, 340 nm, respectively. We have same results compared with the transmission spectrum analysis. In the second part of the experiment, the fabrication of thin film transistors and UV phototransistors are demonstrated by changing the power of targets. In our experiment, we totally realize nine different parameters of thin film transistors. The optimized device, sample E, exhibits the great properties with a μFE of 8.45 cm2/Vs, a SS of 0.43 V/decade, and an on/off current ratio of 4.1×106. And then we apply a-MIO thin film to the thin film transistors, it is found that the performance of the phototransistors are strongly dependent on the In2O3. The cutoff wavelength of the phototransistors is red-shift from 315 nm to 340 nm. The photo-responsivity and DUV-to-visible rejection ratio of the fabricated are 0.39 A/W and 3.1×103. At last, to further enhance the various electrical properties of thin film transistors, so we use two ways to improve. First, because the cuprous oxide is p-type semiconductor then we deposit it on the thin film transistors to be the cap layer. In this design, it is found that thin film transistors is enhanced for electrical properties and stability and it exhibits μFE of 29.8 cm2/Vs, a SS of 0.22 V/decade, and an on/off current ratio of 1.2×106. Compared with the sample E, it is found that we can achieve higher electrical properties. Second, the fabricated of a-MIO thin film transistors is inserted respectively two different buffer layer are demonstrated, and the thin film transistors with Al2O3 buffer layer has better electrical properties. The result can be contributed to the processing method of the buffer layer affects interface quality. As mentioned above two improvement methods, we know that it can enhance thin film transistors properties efficiently.
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Chen, Shu-Yuan, and 陳淑媛. "Morphology and Optoelectronic Property of Organic Field-Effect Transistors from Blends of Poly(3-hexylthiophene) and Biodegradable Poly(lactic acid)." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/dh4925.
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碩士國立臺北科技大學
有機高分子研究所
100
The influence of the solvent on the charge transport and morphology of the polymer blends of poly(3-hexylthiophene) (P3HT) and poly (lactic acid) (PLA), biodegradable polymer, are investigated in this study. The electrical characteristics of blend systems had huge distinction between dichloromethane (CH2Cl2) and chloroform (CHCl3) because their different solubility for P3HT. The films prepared from dichloromethane, poor solvent for P3HT, tended to form well-defined nanowires, attributed to the self-assembly of the P3HT through the solubility-induced process. In the P3HT/PLA blend systems in CH2Cl2, compared with different ratio, the content of P3HT at 10 wt % had mobility of 5.30x10-3 cm2/Vs and on/off ratio of 3.23×103. On the other hand, even the content of P3HT as low as 2 wt % still kept the mobility of 1.76x10-3 cm2/Vs. However, in the blend systems in CHCl3, the mobility decreased dramatically with the increased contents of PLA and there was almost no electrical characteristic at the content of P3HT at 50 wt % due to their sphere phase-separated morphology of P3HT aggregation. These results indicated that we succeed in fabricating the environment-friendly field-effect transistors based on P3HT/PLA blends with low cost and maintaining the device performance using CH2Cl2 as solubility-induced solvent.
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Jhih-ChunSyu and 許至淳. "Investigation of optical and electrical properties of Gallium Zinc Tin Oxide (GaZTO) Thin Film Transistors by RF Sputter and its Optoelectronic Application." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/u3m7xk.
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Dai, Min-Kun, and 戴銘昆. "Optoelectronic properties of single nanowire field effect transistor." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/87889662941355106073.
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碩士國立臺灣大學
物理研究所
98
Fabrication of single nanowire devices and their optoelectronic properties and field effect transistor (FET) characteristics are reported in this thesis. Vapor-liquid-solid growth (VLS) and metal organic chemical vapor deposition (MOCVD) were used to grow three different nanowires: TiO2 nanowires, ,ZnO nanowires, and ZnO / ZnSe core / shell nanowires. Optical lithography and electron beam lithography technology were then used to fabricate single nanowire field effect transistors. For TiO2 single nanowire FET we found that the carrier concentration in the nanowire can be increased by gate bias, and from its FET characteristic we conclude that the TiO2 nanowire grown with ours method is a n-type semiconductor. We also found that the TiO2 single nanowire FET is very sensitive to the light exposure. The on-off ratio of the device current can reach 1000 when the incident light power is 30 mW. From the electric characteristic of ZnO nanowires FET, we found that ZnO nanowires are n-type semiconductors. The on / off current ratio of the ZnO nanowires FET can reach 300 at an incident optical power of 100 mW at an applied voltage of 1 V. After the ZnO wire was coated with ZnSe shell to form ZnO-ZnSe cor-shell nanowire, the light-sensitive of the device increase quite dramatically. We found the current intensity in the ZnO/ZnSe nanowire can increase by 200-fold as compared with the ZnO nanowires in the same light exposure condition. This dramatic increase of the light–induced current is attributed to the charge separation effect in of the type-II band alignment of the ZnO/ZnSe heterostructure.
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Liu, Li-Tsung, and 劉立悰. "Transport and Optoelectronics properties of MoS2 thin film transistors." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/34575185711739466706.
Full textAbstract:
碩士國立中興大學
奈米科學研究所
102
We investigate electrical and optoelectrical properties of a multilayer MoS2 field effect transistor (FET) devices. We use image analysis method, atomic force microscope (AFM), and Raman spectroscopy to identify the thickness and number of layers of the MoS2 flakes, and defined the electrodes by e-beam lithography. The electron mobility deduced from the electrical characteristics of the MoS2 field effect transistor (FET) with a channel length of 4.5 μm and a width of 2.95 μm is about 3.56 cm2V-1s-1 in the air and 5.57 cm2V-1s-1 in vacuum at room temperature. The temperature dependence of the electrical properties indicates that the Schottky barrier between contacts and the MoS2 film significantly affect the electrical performance. We map out the distributions of the photocurrent of the MoS2 devices by using a confocal microscope with a sample stage scanner at the bias voltage of 3 V and the back-gate voltage of 20 V in the air at room temperature. We found that the photocurrent distribution is not symmetric between the source and drain electrodes and the magnitude is dominated by the barrier of the metal-semiconductor interface. The decay of photocurrent of MoS2 TFT can be divided into three stages after the excited source is turned off. The photocurrent first decays rapidly after laser is off because off the electron-hole recombination. And then the photocurrent decreases with a relaxation time about 20 second due to the exciton relaxation and thermoelectric effect. The last part with a relaxation time about 1300 second can be attributed to the slow charge trapping at the surface defect sites of MoS2.
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Chih-WeiLi and 李志偉. "Investigation of ZITO Thin Film Transistor and It’s Optoelectronic Application." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/68053784552432621176.
Full textAbstract:
碩士國立成功大學
微電子工程研究所碩博士班
101
In present study, it is the discussion of zinc oxide based thin film by sputtering. By adjusting the oxygen partial pressure or the sputtering power, the multifunctional thin films will be obtained. In the zinc indium tin oxide films prepared experiments, it is modulating the elements ratio or oxygen pressure to improve the ZnO thin films. First, we applied ZnO thin film as the active layer to the fabrication of TFT with SiO2 gate dielectric. It was found that the field effect mobility was 3.84 cm2/Vs, the threshold voltage of 1.5 V, the subthreshold swing of 0.48 V/decade, the current ratio of 4.6x104. Furthermore, we found that the oxygen partial pressure and the sputtering power would change the optical and electrical properties. Then, we tuned the parameter from the better devices to improve the electrical characteristics. In a short, we doped the ITO into the ZnO thin film to enhance the characteristics of TFTs. In the second part of the experiment, we applied amorphous zinc indium tin oxide film as the active layer to the fabrication of TFT with SiO2 gate dielectric. A-ZITO TFT showed the good performance, like the threshold voltage of 0.9 V, the current ratio of 4.7x105, the subthreshold swing 0.294 V/decade, the field-effect mobility of 5.32 cm2/Vs. In addition, the effect of element composition on the device performance of a-ZITO TFTs was investigated. Then, the exact origin of the improvement of electrical characteristics, and optimize the effects of the In, Zn, and Sn fractions in ZITO thin films, in order to improve the performance of a device. Finally, we did some research about the reliability of the TFTs. After every two weeks, we used the ZnO based TFTs to do some measurements. We found that degeneration of ZITO TFT is more serious. For ZnO TFT and ZITO TFT： the threshold voltage shift of 1.3V, 0.6V; current ratio decrease about one order, three order; subthreshold swing become worse than doubled, three times. In addition, devices would change the characteristics not only for time but also the illumination. We found degradation under the illumination. The ZnO TFTs at a gate voltage of 0 V and a wavelength of 330 nm UV light illumination, the measured current - voltage from 3.0 × 10-9 (A) up to 5.1 × 10-8 (A), the gate bias voltage is 0 V with 330nm light, which are measured according to the photocurrent / dark current of 55 times. In the a-ZITO TFTs, when the gate voltage of 0 V, a wavelength of 330 nm UV light illumination, the measured current - voltage from 5.0 × 10-9 (A) up to 6.1 × 10-7 (A), the bias is 0 V and 330nm light measured under illumination-current / dark current of 87 times.
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Chen, Wei-Tsung, and 陳蔚宗. "Investigation on Metal Oxide Thin Film Transistor for Optoelectronic Devices Application." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/37483348665631368069.
Full textAbstract:
博士國立交通大學
光電工程學系
99
In this study, the fundamental electro-optical characteristics of metal oxide thin film transistor (IGZO TFT) were investigated, and some important derivative devices were also developed. In fact, a high performance IGZO TFT is fabricated easily. However, its variability and instability retard the progress of commercialization. For its instability, it is presented by the behavior of carrier trapping. Either of electron and hole could be trapped at the dielectric surface under an electric field to result the undermined position of threshold voltage. In this study, we attempt to clarify the mechanism of instable behavior of IGZO TFT and reveal how the improving treatments, thermal annealing and passivation, take effect. We have found that the instability is strongly dependent on the oxygen content in IGZO thin film. The instability of IGZO TFT under different polar gate bias stresses will exhibits a symmetric behavior. Higher oxygen content IGZO will correspond to well endurance against negative bias stress and poor endurance under positive bias stress; the TFT with lower oxygen content will exhibit opposite instability behavior. The IGZO TFT with a lower temperature deposited IGZO active layer only can endue one polar bias stress; the stability under another polar bias stress is always poor. The post treatment, thermal annealing, can improve the entire stability under both polar bias stresses. However, the expectation of low temperature fabrication will be destroyed. For its variability, it is presented by the variation in carrier concentration. Any of deposition condition, annealing condition, illumination and surrounding atmosphere could make a change in dopant concentration. Although post thermal annealing can improve the stability of IGZO TFT, the carrier concentration will also be increased or decreased, depends on the furnace atmosphere. Therefore, the annealing conditions like atmosphere should be chose carefully. Besides, strong ultraviolet illumination could make oxygen vacancy to increase the carrier concentration. Therefore, strong ultraviolet can be employed to slightly modulate the oxygen content (the stability under bias stress may be improved) or even make conductive (the conductivity of IGZO can be raised by four orders). The light treated IGZO domain can serve as the source/drain contact in IGZO TFT and its performance is comparable with the metal pad. In this thesis, we propose an assumption different from the common explanation on light effect. We consider that illumination can be regarded as a prompter enhancing the carrier trapping process. Illumination alone will not make the negative shift in threshold voltage. The negatively shifted transfer curve under illuminatin is caused by the applied negative gate bias, which results hole trapping, when scanning the gate voltage. Although IGZO is a transparent material, in fact, it exhibits intense response to light and the effective color ranges from ultraviolet to infrared. Illumination will make dopping process and electron/hole trapping at the dielectric surface. Although IGZO TFT is responsive to visible light and could exhibit a real-time negative photo current caused by electron trapping, we also introduce a light absorption layer in the IGZO TFT to improve the sensibility to visible light. The proposed photo transistor possesses a simple structure; an organic low bandgap material, P3HT (Eg = 2.1 eV), is spun coat on the standard bottom gate IGZO TFT. The P3HT/IGZO junction is a p-n diode and forms a build-in voltage drop across the junction. The excitions will be generated by visible light at the low band gap P3HT layer and the electrons will be injected into the IGZO by the build in electric field to form a back channel. The injected electrons in IGZO possess high mobility to conduct abundant photo current. This proposed photo transistor response to illumination by a positive photo current which is different from the standard device with negative photo current. To date, the drawback of IGZO TFT, limits the realistic application, is the instable behavior. However, for other applications, this drawback may be an advantage. An unstable IGZO TFT, exhibits poor endurance to positive gate bias and have abundant electron trap states, can be fabricated easily at room temperature without post annealing treatment. Possessing abundant electron trap states represents that it is an excellent memory without any intended mechanism for carrier trapping. The writing operation is defined as a VG pulse (VG = 20 V, 20s) to move the transfer curve in the direction of positive gate voltage; the erasing operation is defined as an illumination accompanied VG pulse (VG = - 20 V, 20s, UV) to move the transfer curve in the direction of negative gate voltage. This proposed memory exhibits a significant threshold voltage window of 30 V and an on/off ratio of 105. Furthermore, this device performs well repeatability under writing/erasing cycles. Another feasible application of this device is the real-time photo detector. The UV made negative shift in threshold can be compensated by positive VG pulses promptly, which leads to a real-time photo transistor. In fact, generally photo transistors are unable to perform real-time sensing. The proposed real-time photo detector in this thesis has a significant light/dark ratio of 105. This is the best metal oxide based photo detector nowadays. Another important device for application is inverter. If we attempt to fabricate a basic logic unit, inverter, using metal oxide based transistors, we will face a problem of the unfeasibility of CMOS structure because the lack of p-type metal oxide material. Therefore the threshold voltage modulation seems the unique solution. Threshold voltage modulation can be achieved by a conventional dual gate structure. In this study, we propose a novel dual gate TFT using a floating metallic back gate; the gate is floating, implying additional power supply is not necessary during device operation. The bias provided by floating gate to IGZO body comes from the work function difference. Since there is almost no dielectric layer located between floating gate and IGZO, the controllability of floating gate to IGZO body is much high; a little build in voltage can bring a noticeable threshold voltage shift. No matter depletion mode and enhance mode TFTs with excellent performance can be fabricated using this dual gate structure. The advantages of this dual gate device are high performance, unnecessary of additional power supply and unnecessary of additional dielectric layer. Finally, a high performance inverter comprised of the proposed dual gate TFTs is demonstrated in this study.
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Baek, Eunhye. "Multi-functional Hybrid Gating Silicon Nanowire Field-effect Transistors: From Optoelectronics to Neuromorphic Application." 2018. https://tud.qucosa.de/id/qucosa%3A72327.
Full textAbstract:
Enormous demands for fast and low-power computing and memory building blocks for consumer electronics, such as smartphones or tablets, have led to the emergence of silicon nanowire transistors a decade ago. Along with the Si-based nanotechnology, the silicon compatible optical and chemical sensing applications have boosted the research on hybrid devices that combine the organic and inorganic materials. Apart from the revolution in the device dimensions, the rapid growth of artificial intelligence in the software industry brunch requires the next generation’s computers with the revolutionized hybrid device architecture. Implementing such new devices can effectively perform machine learning tasks without the massive consumption of energy. The hybrid Si nanowire devices have an excellent capability to replace the conventional computing element by providing new functionalities of combined materials to the traditional transistor devices preserving the advantage of CMOS technology.
A goal of this thesis is to develop functional hybrid Si nanowire-based transistors modulated by the stimuli-dependent gate to go beyond the current digital building blocks. The hybrid devices converge semiconductor channel and various materials from organic molecules to silicate composite as a gate of the transistor. External stimuli change the electronic state of the gate materials which is transformed to the gate potential of the transistors.
First, this thesis studies the electronic characteristics of the Si nanowire FETs under the optical stimulus. Optical stimulus induces the strong conductance change on bare Si nanowire FETs. Under the light with low power intensity, the transistor shows an unconventional negative photoconductance (NPC) which is dependent on the doping concentration of the nanowire and the wavelength of the incident light. The dopants ions and surface states cause photo-generated hot electrons trapping which restricts conventional photoconductance in the semiconductor.
In the hybrid device, however, the gate material on the Si dioxide layer plays a significant role in the optoelectronic modulation of the FET device. This thesis demonstrates that an organic photochromic material, porphyrin, wrapping around the nanowire channel acts as an optical gate of the Si nanowire transistor. The diffusive property of electrons in the molecular film decides the optical switching dynamics and efficiency.
Further, this thesis introduces new functional gate material, sol-gel derived ion-doped silicate film, based on the availability of stimulus-dependent gate modulation. This amorphous and transparent silicate film shows memristive property due to the ionic redistribution in the film under bias condition. Interestingly, the sol-gel film-coated Si nanowire FETs the devices show a double gate effect cooperating with a back gate under light illumination which is due to the channel separation in the fin structure of the nanowire.
In addition, the sol-gel silicate film-coated Si nanowire transistor emulates the neuronal plasticity with pulsed gate stimulation, namely “neurotransistor.” Because of the mobile ions in the silicate film, the transistor has a short-term memory and mimics membrane potential change of the neuron cell. The neurotransistor could be used as a computing node in the physical neural network for hardware machine learning.
This work demonstrates that the physical properties of the gate material decide the transfer characteristics and time-dependent dynamics of the hybrid Si nanowire transistors. The optical and neuromorphic gate features of the hybrid transistors would accelerate the advancement of an optical or brain-like computing machine.
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Li, Yi-Fen, and 李宜芬. "An Optoelectronic Biosensor for Overcoming the Debye Screening Effect in Field-Effect Transistor Biodetections." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/gy94wc.
Full textAbstract:
碩士國立臺灣大學
化學研究所
106
Field-effect transistors (FETs) have long been employed as high-sensitive biosensors for detecting biomolecules, but they also encounter a stringent challenge of the Debye screening effect on the signal detection in physiological buffers, which hinders the further applications of FETs in clinical diagnosis. For the Debye screening effect, because the ions and charged molecules in a high-salt buffer, e.g., human serum or urine, will shield the interacting potential exerted by the charged targets toward the sensing channel of an FET, the signals are severely attenuated. To overcome this difficulty, we developed an innovative optoelectronic biosensor, which is able to detect targeted biomarkers in high concentrated buffers, like 10× phosphate buffered saline (PBS) with a Debye length of ~0.23 nm and 10× N-methyl-d-glucamine (NMG) buffer with a Debye length of ~0.7 nm. The working principle of this newly designed optoelectronic FET biosensor is based on the fact that the FETs are excited by light rather than by electric field in traditional FETs. Since the penetration of light in a concentrated electrolytic environment is not strictly impeded, the signals of photo-induced currents in the optoelectronic FETs can be well detected. Our optoelectronic biosensor is composed of a 2D layered semiconductor crystal (tin disulfide, SnS2)-fabricated FET in conjunction with upconverting nanoparticles (UCNPs) via aptamer linkers (referred to as UCNP/SnS2-FET). In a UCNP/SnS2-FET biosensor, the aptamer also acts as a receptor for detecting a specific target. When binding with the target, the aptamer is entangled to shorten the distance between UCNPs and the SnS2-FET; consequently, the upconverted green emission (~530 nm) from 980 nm-excited UCNPs irradiates more intensively on the SnS2-FET (with a bandgap of 2.2 eV ~ 560 nm), resulting in a signal change. By recording the signal change in the SnS2-FET, targeted biomarkers can be detected and quantified. The aim of this research is to investigate the feasibility, sensitivity, and detection limit of a UCNP/SnS2-FET biosensor by detecting two targeted biomolecules: dopamine and potassium ion. The experimental results demonstrate that we can successfully detect 1 pM of dopamine and 10 pM of potassium ions in 1× PBS and 10× NMG buffer, respectively.
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Chou, Cheng-Yun. "III-V Semiconductor Materials Grown by Molecular Beam Epitaxy for Infrared and High-Speed Transistor Applications." Thesis, 2016. https://doi.org/10.7916/D8J38SPJ.
Full textAbstract:
Semiconductor devices based on III-V materials have been the focus of intense research due to their superior electron mobility and favorable energy direct bandgap which are applicable in infrared wavelength range optoelectronics and high speed electronic systems. The thesis presented here consists of two thrusts; the first focusing on infrared applications, and the second focusing on InP-based heterojunction bipolar transistors (HBTs). In the first thrust, we investigate type-II InAs/GaSb superlattice IR detector devices and the effect of substrate orientation on InSb and InAs nanostructure morphology. In the second thrust, we study InP-based high frequency HBTs. A low resistance InAs ohmic contact is demonstrated, and we presented along with a study of the crystalline qualities in GaAs0.5Sb0.5 films grown on tilted- axis InP substrates.
Chapter 2 presents fabrication and characterization of two type-II superlattice structures with 15 monolayer (ML) InAs/12ML GaSb and 17ML InAs/7ML GaSb grown on GaSb (100) substrates by solid-source molecular beam epitaxy (MBE). The X-ray diffraction (XRD) measurements of both the 15ML InAs/12ML GaSb and 17MLInAs/7ML GaSb superlattices indicated excellent material and interface qualities. The cutoff wavelengths of 15ML InAs/12ML GaSb and 17ML InAs/7ML GaSb superlattices photodetectors were measured to be 6.6μm and 10.2μm, respectively. These different spectral ranges were achieved by growing alternating layers of varying thicknesses which allowed for bandgap engineering of the superlattices of InAs and GaSb. Lastly, a mid-IR type-II superlattice photodiode was demonstrated at 80K with a cutoff wavelength at 6.6µm. The device exhibited a near background limited performance (BLIP) detectivity at 80K and higher temperature operation up to 280K.
In Chapter 3, we show that the (411) orientation, though not a naturally occurring surface, is a favorable orientation to develop a buffer layer into a super flat surface at a certain high growth temperature. The (411) surface is a combination of localized (311) and (511) surfaces but at a high growth temperature, adatoms can obtain enough energy to overcome the energy barrier between these localized (311) and (511) surfaces and form a uniform (411) surface with potential minima. This results in a super flat surface which is promising for high-density nanostructure growth. In this work, this is the first time that the highest InSb and InAs nanostructures density can be achieved on the (411) surface which is in comparison with the (100), (311), and (511) surfaces.
Chapter 4 of this thesis addresses the use of an InAs layer as a low-resistance ohmic contact to InP-based heterostructure devices. Selective area crystal growth of InAs on a dielectric (Benzocyclobutene, BCB polymer) covered InP (100) substrate and direct growth of InAs on InP substrate were performed by MBE. Heavy doping of InAs using Te was carried out to determine the lowest sheet resistance. Based on scanning electron microscope (SEM) and XRD measurements, increasing substrate temperature from 210 ℃ to 350 ℃, led to an improvement in crystallinity from a polycrystalline layer to a single crystal layer with a corresponding improvement of surface morphology. Moreover, a narrow X-ray diffraction peak indicated full-relaxation of the inherent 3.3% lattice-mismatch in InAs/InP layers. Furthermore, around 290 ℃ a tradeoff was reached between crystallinity and optimized dopant incorporation of Te into InAs for the lowest sheet resistance.
Lastly, Chapter 5 discusses the effect of substrate tilting on the material properties of MBE grown GaAsSb alloys closely lattice-matched to an InP substrate. InP(100) substrates tilted 0°off-(on-axis), 2°off-, 3°off-, and 4°off-axis were used for MBE growth; then the material qualities of GaAsSb epitaxial layers were compared using various techniques, including high resolution XRD, photoluminescence (PL) and transmission-line measurements (TLM). Substrate tilting improved the crystalline quality of the GaAsSb alloys, as shown by a narrower XRD linewidth and enhanced optical quality as evidenced by a strong PL peak. The results of TLM show that the lowest sheet resistance was achieved at a 2° off-axis tilt.
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Xu, Xiangming. "Wafer-scale growth method of single-crystalline 2D MoS2 film for high-performance optoelectronics." Diss., 2020. http://hdl.handle.net/10754/666313.
Full textAbstract:
2D semiconductors are one of the most promising materials for next-generation electronics. Realizing continuous 2D monolayer semiconductors with single-crystalline structure at the wafer scale is still a challenge. We developed an epitaxial phase conversion (EPC) process to meet these requirements. The EPC process is a two-step process, where the sulfurization process was carried out on pre-deposited Mo-containing films. Traditionally, two-step processes for 2D MoS2 and other chalcogenides have suffered low-quality film and non-discontinuity at monolayer thickness. The reason was regarded as the low lattice quality of precursor film. The EPC process solves these problems by carefully preparing the precursor film and carefully controlling the sulfurization process. The precursor film in the EPC process is epitaxial MoO2 grown on 2″ diameter sapphire substrate by pulsed laser deposition. This epitaxial precursor contains significantly fewer defects compared to amorphous precursor films. Thus fewer defects are inherited by the EPC MoS2 film. Therefore, EPC MoS2 film quality is much better. The EPC prepared monolayer MoS2 devices to show field-effect mobility between 10 ~ 30 cm2·V-1s-1, which is the best among the two-step process. We also developed a CLAP method further to reduce the defects in the precursor oxide film; thus, in-plane texture in the thicker MoS2 film was eliminated, and a single-crystalline structure was obtained in the wafer-scale MoS2 films. The potentially feasible technique to further improve the 2D film quality is pointed out for our next research plan. Meanwhile, the epitaxial phase conversion process was proposed to be as a universal growth method. Last but not least, we demonstrate several potential applications of the wafer-scale single-crystalline MoS2 film we developed, such as logic circuits, flexible electronics, and seeding layer of van der Waal or remote epitaxial growth.
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Ullberg, Nathan. "Characterizing optical and electrical properties of monolayer MoS2 by backside absorbing layer microscopy." Thesis, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-419630.
Full textAbstract:
Nanomaterials are playing an increasing role in novel technologies, and it is important to develop optical methods to characterize them in situ. To that end, backside absorbing layer microscopy (BALM) has emerged as a powerful tool, being capable to resolve sub-nanometer height profiles, with video-rate acquisition speeds and a suitable geometry to couple live experiments. In the internship, several techniques involving BALM were developed, and applied to study optical and electrical properties of the transition metal dichalcogenide (TMD) monolayer MoS2, a type of 2-dimensional (2D) crystalline semiconductor. A simulations toolkit was created in MATLAB to model BALM, a workflow to reliably extract linear intensities from the CMOS detector was realized, and 2D MoS2 was synthesized by chemical vapor deposition followed by transfer to appropriate substrates. BALM data of the 2D MoS2 was acquired and combined with simulations, giving a preliminary result for its complex refractive index at 5 optical wavelengths. In addition, the first steps towards coupling BALM with a gate biased 2D MoS2 field-effect transistor were explored. To complement BALM measurements, the grown samples were also characterized by conventional optical microscopy, scanning electron microscopy, atomic force microscopy, photoluminescence spectroscopy, and Raman spectroscopy. This work provides new additions to an existing platform of BALM techniques, enabling novel BALM experiments with nanomaterial systems. In particular, it introduces a new alternative for local extraction of optical parameters and for probing of electrical charging effects, both of which are vital in the research and development of nano-optoelectronics.