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Dissertations / Theses on the topic 'OPTOELECTRONIC DEVICE APPLICATIONS'
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1
Guptah, Vinod Kumar. "Growth on patterned substrates for optoelectronic device applications." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267027.
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Alexandropoulos, Dimitrios. "Theoretical studies of GaInNAs for optoelectronic device applications." Thesis, University of Essex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274313.
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Pratt, Andrew Richard. "Control of indium migration on patterned substrates for optoelectronic device applications." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307775.
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Grudowski, Paul A. "The metalorganic chemical vapor deposition of III-V nitrides for optoelectronic device applications /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Xin, Huoping. "Gas-source molecular beam epitaxy of GaInNAs and Ga(In)NP for electronic and optoelectronic device applications /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9970681.
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Kim, Danny. "Dry passivation studies of GaAs(110) surfaces by Gallium Oxide thin films deposited by electron cyclotron resonance plasma reactive molecular beam epitaxy for optoelectronic device applications." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ63140.pdf.
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Cheung, Chor-keung. "The construction of a focused low energy positron beam facility and its application in the study of various optoelectronic materials." View the Table of Contents & Abstract, 2006. http://sunzi.lib.hku.hk/hkuto/record/B36995770.
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Cheung, Chor-keung, and 張初強. "The construction of a focused low energy positron beam facility and its application in the study of various optoelectronic materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37434925.
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Li, Cheng. "Metal oxide films for optoelectronic device application." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648598.
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Davis, Nathaniel J. L. K. "Applications of spectral management in optoelectronic devices." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/263670.
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The application and efficiency of optoelectronic devices depends on the ability to control the absorption and emission processes of photons in semiconductors. This thesis looks at three different applications of spectral management across a broad range of optoelectronic devices: photovoltaics (PVs), luminescent solar concentrators (LSCs) and light-emitting diodes (LEDs). Multiple excitation generation (MEG) – a process in which multiple charge-carrier pairs are generated from a single optical excitation - is a promising way to improve the photocurrent in photovoltaic devices and offers the potential to break the Shockley-Queisser limit. Here we present solar cells fabricated from PbSe nanorods which show external quantum efficiencies exceeding 100 %. This demonstrates the potential for substantial improvements in PV device performance due to MEG. Through spatial and spectral concentration, LSCs have the potential to reduce the cost of photovoltaic energy production and are attractive prospects for photobioreactors and building-integrated applications. Here we introduce versatile star-shaped donor-acceptor molecules based on a central BODIPY acceptor with oligofluorene donor side units. We perform comprehensive device measurements and Monte Carlo ray tracing simulations of LSCs. We find that the measured structures permit waveguide propagation lengths on a par with state-of-the-art nanocrystalline emitters, while proposed hypothetical structures can be seen as viable candidates for photobioreactor and energy production roles and should be synthesized. The efficiency of nanocrystal-based LEDs is inherently limited by the types of crystals used. Cesium lead halide perovskite nanocrystals exhibit photoluminescence quantum efficiencies approaching 100%. However, due to the large surface areas and anion mobility halogen exchange between perovskite nanocrystals of different compositions occurs rapidly, limiting applications. Here, we report significantly reduced halide exchange between chloride and iodide CsPbX3 (X= Cl, I) perovskite nanocrystals. We investigate perovskite-based multi-crystal component samples and their resulting optical and electrical interactions in bulk heterojunction LEDs. Efficient photon reabsorption from CsPbCl3 to CsPbI3 nanocrystals was found to improve LED device performance.
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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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Jones, Gareth Francis. "Modification of graphene for applications in optoelectronic devices." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/31537.
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In this thesis, we investigate how the optical and electronic properties of graphene may be modified in proximity to various other materials. We present several examples of how modification in this way can help make graphene better suited for specific device applications. We develop a method of up-scaling the fabrication of FeCl3-intercalated few-layer graphene from micron-sized flakes to macroscopic films so that it may be used as a transparent electrode in flexible light-emitting devices. We also find that photo-responsive junctions can be arbitrarily written into FeCl3-intercalated few-layer graphene by means of optical lithography. These junctions produce photocurrent signals that are directly proportional to incident optical power over an extended range compared to other graphene photodetectors. Through theoretical analysis of these junctions, we conclude that the enhanced cooling of hot carriers with lattice phonons is responsible for this behaviour. Finally, we trial rubrene single crystals as the light-absorbing layer in a graphene phototransistor. We find that rubrene single crystal-graphene interfaces exhibit enhanced charge transfer efficiencies under illumination with extremely weak light signals. Through a comparative study with similar devices, we conclude that the wide variation in sensitivity amongst graphene phototransistors is largely due to extraneous factors relating to device geometry and measurement conditions.
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Lee, Min-Hsuan. "Solution-processable organic-inorganic hybrid transparent electrode for optoelectronic applications." HKBU Institutional Repository, 2016. https://repository.hkbu.edu.hk/etd_oa/320.
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The aim of this PhD thesis is to undertake a comprehensive research to study the optical, electrical, surface electronic and morphologic properties, formulation and surface modification of solution processable organic-inorganic hybrid transparent electrodes as well as their applications in optoelectronic devices. In this study, MoO3 nanoparticles and graphene oxide (GO) nanosheets were incorporated into the poly(3,4-ethylenedioxythiophene) -poly(styrenesulfonate) (PEDOT:PSS) layer forming a hybrid anode interfacial layer (AIL) and subsequently a hybrid transparent electrode of AIL/silver nanowires (AgNWs), significantly improved charge injection in CdSe/ZnS-based quantum dot-light emitting diodes (QD-LEDs) and charge collection in bulk heterojunction (BHJ) organic solar cells (OSCs). The effect of oxidation behavior and charge transfer between PEDOT and MoO3, as well as PEDOT and GO, on the enhancement in conductivity of hybrid PEDOT:PSS-MoO3 and PEDOT:PSS-GO AILs was investigated systematically. The presence of a PEDOT:PSS-MoO3 AIL promotes a good interfacial contact between the hole transporting layer (HTL) and the solution-processed hybrid transparent electrode for efficient operation of QD-LEDs. This work reveals that the use of the hybrid PEDOT:PSS-MoO3 AIL benefits the performance of QD-LEDs in two ways: (1) to assist in efficient hole injection, thereby improving luminous efficiency of QD-LEDs, and (2) to improve electron-hole current balance and suppression of interfacial defects at the QD/electrode interface. The surface wettability of the PEDOT:PSS-MoO3 AIL was controlled successfully for making a good contact between the HTL and the AgNWs, enabling efficient charge injection or charge collection, and thereby improvement in the device performance. The effect of PEDOT:PSS-GO AIL on the performance of transparent QD-LEDs was also analyzed. The maximum brightness of the transparent QD-LEDs, made with a solution-processed hybrid top transparent electrode of PEDOT:PSS-GO/AgNWs, is 3633 cd/m2 at 15 V, comparable to that of a structurally identical control QD-LED made with an evaporated Ag electrode, with a brightness of 4218 cd/m2 operated under the same condition. The change in the hydrophobicity of the PEDOT:PSS-GO AIL, e.g., from the hydrophobic to hydrophilic characteristics, was observed. The interaction between PEDOT and GO nanosheets induces the transition between benzoid-quinoid structures, contributing to the enhanced charge carrier transport via the PEDOT:PSS-GO AIL. The energy level alignment at the HTL/electrode interface and the excellent electrical conductivity of PEDOT:PSS- GO/AgNWs transparent electrode result in an obvious improvement in the performance of QD-LEDs. Transparent QD-LEDs also demonstrated remarkable efficiency via cathode interfacial engineering. Two cathode interfacial modifications include incorporating (1) a hybrid bathophenanthroline (Bphen):Cs2CO3-based electron transporting buffer layer (EBL) and (2) a conjugate polymer of poly[(9,9-bis(3'-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7- fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN-Br)-based EBL. The approach of n-doping effect in the BPhen:Cs2CO3 EBL not only modifies the surface electronic properties of the ZnO electron transporting layer (ETL) but also improves the electron injection at the QD/cathode interface. The n-doping mechanism in the Bphen:Cs2CO3 EBL was investigated. PFN-Br EBL has also been employed to tune the surface work function of ZnO ETL. It was observed that the ZnO/PFN-Br formed an interfacial dipole at the ETL/QD interface, which is suitable for efficient electron injection in the transparent QD-LEDs. In order to improve electron-hole current balance, a GO/MoO3-based multilayer AIL was adopted facilitating efficient charge transfer through improved energy level alignment at the HTL/hybrid electrode interface. Photoelectron spectroscopy revealed tuned surface work function with reduced interfacial barrier for efficient hole injection in transparent QD-LEDs. In these devices, the cathode and anode interfacial modifications have been optimized and studied. This study was also extended to investigate the effect of the organic-inorganic hybrid electrode on performance enhancement of all solution processable organic solar cells (OSCs). The reduction in series resistance and increase in shunt resistance of solution-processed OSCs originated from improved contact selectivity as well as enhanced charge collection efficiency. These properties are reflected in the significantly improved fill factor and short-circuit photocurrent density for the all solution-processed OSCs. Enhanced charge collection at the BHJ/electrode interfaces and improved process compatibility are mainly responsible for efficiency improvement in the cells. The outcomes of this work would allow further advances in device performance. This research also highlights the need to explore interfacial electronic properties and reduce energetic barrier at BHJ/electrode interfaces in fully solution-processed OSCs through photoelectron spectroscopy measurements. The results of this research demonstrate that the solution processable organic-inorganic hybrid transparent electrode developed in this work is beneficial for application in fully solution-processed optoelectronic devices.
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Drew, Stephen. "Symmetric Gain Optoelectronic Mixers for LADAR Applications." Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/DrewS2009.pdf.
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Lee, Jeffrey Chi Wai. "Chiral photonic crystals and their potential applications /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202009%20LEE.
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Cheung, Yuk Lung. "Application of silicon display for photo printer /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202004%20CHEUNG.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 80-82). Also available in electronic version. Access restricted to campus users.
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Lee, Siew-wan Alex. "Optical properties of intermixed quantum wells and its application in photodetectors /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21326411.
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Ishibashi, Jacob Shotaro Afaga. "BN Isosteres of Acenes for Potential Applications in Optoelectronic Devices." Thesis, Boston College, 2017. http://hdl.handle.net/2345/bc-ir:107613.
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Thesis advisor: Shih-Yuan LiuThis dissertation describes progress in the field of polycyclic boron- nitrogen-containing systems, especially for potential application in organic-based optoelectronic devices and hydrogen storage materials. The replacement of a BN unit for a CC unit organic compounds (BN/CC isosterism) can have a profound effect on the electronic structure and even function of a given molecular topology without changing its physical structure very much. Direct comparison between a BN-containing molecule and its direct all-carbon analogue is crucial to establishing the origin of these differences. The synthesis and optoelectronic characterization of boron- nitrogen-containing analogues of naphthalene, anthracene, and tetracene are disclosed. Also examined herein is the aromatic Claisen rearrangement applied to an azaboryl allyl ether. Finally, the chemistry of saturated BN heterocycles, including an iridium-catalyzed transfer dehydrogenation method for synthesizing BN-fused azaborines. Also disclosed is the actual application of these cyclic amine-boranes in supplying hydrogen for a proton exchange membrane (PEM) fuel cell
Thesis (PhD) — Boston College, 2017
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Tse, Chui-wan. "Rhenium containing hyperbranched polymers for photonic applications." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B38574512.
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Montero, Martín Jose María. "Charge transport in organic semiconductors with application to optoelectronic devices." Doctoral thesis, Universitat Jaume I, 2010. http://hdl.handle.net/10803/10474.
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El estudio del transporte de carga en semiconductores orgánicos contribuye al desarrollo y optimización de LEDs orgánicos y nuevas células solares. En OLEDs de un sólo portador se ha encontrado una fórmula explícita de la característica densidad de corriente y potencial (J-V) con movilidad dependiente del campo eléctrico. Un test para diferenciar la movilidad dependiente del campo y de la densidad ha sido dado por medio de una ley universal de escalado. Los espectros de capacidad y los tiempos de tránsito han sido examinados con la inclusión de la movilidad dependiente del campo eléctrico y comparado con los datos experimentales, verificándose el modelo teórico planteado. Se ha descrito la movilidad de portadores de carga a través de un modelo de transporte con una densidad exponencial de trampas. Se han utilizado técnicas de espectroscopía de impedancia para explicar la movilidad dependiente del campo eléctrico en términos del múltiple atrapamiento ejercido por los estados energéticamente localizados. Este modelo ha explicado de forma coherente los espectros de capacidad recogidos en medidas experimentales, particularmente su comportamiento a bajas e intermedias frecuencias. La respuesta de los OLED (polímero SY) ha sido estudiada en los regímenes estacionario y transitorio. En el régimen estacionario, se han descrito las corrientes de fuga a bajos potenciales. Se ha
analizado la existencia de mayor corriente circulando por el perímetro que por el área del dispositivo. En el régimen transitorio, se ha
proporcionado una explicación sobre las colas de luz emitida observadas al cesar la perturbación de potencial escalón: procede de la inyección
limitada de electrones en el cátodo.
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Chun, Carl S. P. (Shun Ping). "Investigation of GaAs MESFET amplifier topologies for optoelectronic receiver applications." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/14813.
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Sustersic, Nathan Anthony. "The growth and characterization of silicon-germanium devices for optoelectronic applications." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 3.10 Mb., 83 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435828.
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Gan, Haiyong. "Electro-optic Polymer Based Fabry-Perot Interferometer Devices for Optoelectronic Applications." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/195839.
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Fabry-Perot interferometer (FPI) devices are designed based on the electro-optic (EO) activities of nonlinear optical (NLO) polymer materials for tunable optical filters (TOFs) and spatial light modulators (SLMs). The performance of the EO polymer based FPI devices is theoretically modeled with first order approximation on the FPI cavity interface phase dispersion. NLO materials including TCBD coupled hybrid sol-gel, AJL8/amorphous polycarbonate (APC), and AJLS102/APC are incorporated in FPI structures with distributed Bragg reflector mirrors and transparent conducting oxide electrodes for TOFs. High finesse (over 200), low drive voltage (10 dB isolation ratio with 5 V), and fast settling time (about sub-millisecond) are achieved. The physical origin of the large tunabilities is explored and the contributions from EO effect and inverse piezoelectric effect are analyzed. EO polymer SWOHF3ME/APC is employed in FPI devices with simplified structures for SLMs. Modulation beyond megahertz level is achieved with constant modulation ratio from DC frequency to high operation speed. The operation speed can be potentially over gigahertz with improved device and drive circuit design. When the EO polymer based SLM is configured to work at near the resonance band of the NLO material, the spectral tunability is increased due to resonance enhanced EO activity and the SLM performance is significantly improved. The EO polymer based FPI devices can be further optimized and are promising candidates for many optoelectronic applications.
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Tse, Chui-wan, and 謝翠雲. "Rhenium containing hyperbranched polymers for photonic applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B38574512.
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Zaidi, Tahir. "Ferromagnetic and multiferroic thin films aimed towards optoelectronic and spintronic applications." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/41110.
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This work targeted the growth of gadolinium (Gd)-doped gallium nitride (GaN) thin films (Ga₁₋ₓGdₓN) by metal organic chemical vapor deposition (MOCVD). Characterization and evaluation of these Ga₁₋ₓGdₓN thin films for application in spintronics/optoelectronics devices also formed part of this work. This work presents: (1) the first report of stable, reproducible n- and p-type Ga₁₋ₓGdₓN thin films by MOCVD; (2) the first Ga₁₋ₓGdₓN p-n diode structure; and (3) the first report of a room temperature spin-polarized LED using a Ga₁₋ₓGdₓN spin injection layer. The Ga₁₋ₓGdₓN thin films grown in this work were electrically conductive, and co-doping them with Silicon (Si) or Magnesium (Mg) resulted in n-type and p-type materials, respectively. All the materials and structures grown in this work, including the Ga₁₋ₓGdₓN-based p-n diode and spin polarized LED, were characterized for their structural, optical, electrical and magnetic properties. The spin-polarized LED gave spin polarization ratio of 22% and systematic variation of this ratio at room temperature with external magnetic field was observed.
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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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Rezaei, Mazinani Shahab. "Development of novel organic optoelectronic technologies for biomedical applications." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEM028/document.
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Les dispositifs optoélectroniques organiques possèdent plusieurs avantages pour les applications dans le domaine du biomédical. Le photodétecteur organique (OPD) est un type de dispositif optoélectronique qui n’est pas encore utilisé pour la détection d’activité cérébrale. L’objectif de cette thèse a été d’explorer l’utilisation des OPD, constitués de différent matériaux donneur-accepteur d’électrons, dans le domaine des neurosciences. Nous avons présenté différent types d’OPD possédant une structure minimale, une excellente sensibilité et un grand potentiel d’intégration dans les méthodes de microfabrication existantes. Les détecteurs organiques ont été utilisés pour l’enregistrement de signaux optiques intrinsèques et de signaux fluorescents reflétant l’activité du calcium dans le cerveau. De plus, un autre aspect des OPD est présenté (en combinaison avec les transistors électrochimiques organiques (OECT)) : des systèmes électroniques biomimétiques basé sur une architecture électronique neuro-inspirée. Cette thèse démontre le potentiel des OPD pour enregistrer des activités cérébrales. Elle ouvre une nouvelle perspective, grâce à leur grande sensibilité, comme capteur optique en combinaison avec des dispositifs neuronaux implantables. Ceci élargira les frontières de l’électrophysiologie optique pour explorer les mécanismes complexes du cerveau et des maladies neurodégénérativesOrganic optoelectronic devices have many promising qualities for biomedical applications. Organic photodetectors (OPD), one type of such devices, have yet to be utilized for the detection of signals in the brain, to the best of our knowledge. The goal of this thesis was to explore the use of OPDs, based on different electron-donor and -acceptor materials in neuroscience applications. Different types of minimal-structure OPDs are presented, which have an excellent sensitivity and a high potential for incorporation into existing microfabrication methods. The organic sensors were utilized for monitoring the brain’s intrinsic optical signals and fluorescent calcium dynamics. Additionally, another aspect of these devices is presented (in combination with organic electrochemical transistors (OECT)): neuroinspired electronics, electronics that mimic biology. This thesis establishes the promise of OPDs for monitoring brain activities, which would lead to their integration, as high-sensitive micron-scale optical sensors in organic neural probes. Such device would result in exploring optical biological activities in the deep brain on the cellular level and would push the frontiers of optical-electrophysiology by giving a better understanding of complex mechanisms of the brain function and neurodegenerative diseases
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劉彥泓. "Nano Texturization by Plasma for Optoelectronic Device Applications." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/17582493898868985462.
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Hsu, Tsung-Han, and 許宗翰. "Study of Metal Silicide amd Nanomaterials for Optoelectronic Device Applications." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/97783933953231557789.
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碩士國立臺灣大學
材料科學與工程學研究所
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Metal silicide and photonic crystals play important roles in optoelectronic devices. In this thesis, we study optical properties of these two kinds of materials. The first part of thesis is metal silicide, titanium silicide with. Titanium silicide is very suitable as gate materials in next-generation photo detector for its good thermal stability and lowest sheet resistance among all of metal silicides. We characterize the optical properties , reflective index and extinction coefficient, of titanium silicide by ellipsometryin the visible regime for photodetector application. Since ArF laser (193nm) and F2 laser (157nm) are light sources of optical lithography for the generation of less than 100 nm , we also characterize optical constants of titanium silicide in the 193nm and 157nm wavelength regimes. We find titanium silicide has high reflectance in the wavelength regime 450nm~750nm, which is an important range for photodetector. Therefore, we designe and fabricate an antireflective coatings for wavelength between 450nm~750nm, then the reflectance in the range is reduced to less than 5%. For optical lithography application, we also fabricate bottom antireflective coatings of titanium silicide in 193nm and 157nm for the reduction of standing-wave effect.. In the photonic crystals study, we use well-mixed colloidal nanomaterial in different sizes to form binary opals. By this method, we can fine-tune the photonic bandgap within 1~2nm. Besides, by changing the size and contents of the small colloids, we can be aware of how the smaller one affects the bandgap and crystal structure of binary opals. We also find the smallest size of doped collide has significant effect.
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YING, CHOU CHENG, and 周承穎. "Development of flexible conductive thin films for optoelectronic device applications." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/85557505423796081260.
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碩士國立臺灣師範大學
機電科技學系
101
The aim of this study is to use a simple process with a lift-off and electrophoresis plating technique to fabricate the conductive thin film on flexible substrate with CNTs (Carbon nanotubes). The CNTs are studied as the electrode material and have the potential owing to its high conductivity and the convenience of the fabricating process. To deploy the CNTs, we apply SDS (Sodium dodecyl sulfate) as the dispersant. Here, the substrate is employed PDMS (Polydimethylsiloxane), which is a group of polymeric organosilicon compounds. For the direct photolithography on PDMS, the surface of PDMS should be not only hydrophilic, but more flat so that the photoresist could be spun on the surface evenly. After the process of photolithography, the patterns of electrode can be defined on the surface. Based on this direct process, the complicated electrode patterns can be easily defined and its pattern would not be deformed. In electrophoretic plating technique, by applying different voltages and time for abtained optimized parameters, it can be deposited CNTs on PDMS well. After depositing, the CNTs can be transferred to PDMS. Finally, we use SEM, FTIR, and Raman Spectrum for measuring the surface and properties of CNT. Therefore, this study provides a novel and simple way to fabricate the conductive thin films and through the complicated electrode pattern defined, the application of thin films for photoelectric sensors could be easily used in this work.
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Hsieh, Hsien-Chieh, and 謝顯傑. "Development of functional light-extraction microstructure for optoelectronic device applications." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/44016878160469140278.
Full textAbstract:
碩士國立臺灣師範大學
機電科技學系
101
With the increasing downscaling of electro-optical components and the development of microelectromechanical systems (MEMS), microlens array is attracting more attention for various applications, including optical communications, image processing, lab-on-a-chip techniques, high-definition projection displays and other photonic devices. Hence, many manufacture processes for microlens have been described, such as the thermal reflow, laser micromachining, gay-scale mask, ink-jet printing and proton beam writing. The variety of microlens array can usually be employed for lighting design for improving their outcoupling efficiency or enhancing the light extraction efficiency. Compared with the conventional photolithography, a diffuser approach can be used in developing a process to fabricate the microlens array. The advantages of a diffuser include a simple process and shape control of microlens array. This study presents a simple and effective diffuser approach to fabricate a plastic microlens array with controllable shape and full fill-factor, and combined the methods of the soft lithography and plastic replication. It can be found that the microlens array of PDMS structures is an extremely high full fill-factor. The fill-factor in this study is approximately 100%. In conclusion, the full fill-factor PDMS microlens array can be successfully fabricated by a diffuser approach. The precise shape of microlens is needed by using the well-controlled process parameters. The curves of the microlens are fitted by using sag equation. Thereupon, this study can be helpful to a new route to range of functional optical applications.
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Wu, Hung-Chin, and 吳泓錦. "Side Chain Engineering on Polymeric Semiconductors for Optoelectronic Device Applications." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/32858534823016129730.
Full textAbstract:
博士國立臺灣大學
化學工程學研究所
103
Polymeric semiconductors have received great attentions for organic electronic and optoelectronic devices, such as field-effect transistors (FETs), photovoltaic cells (PVs), and memory devices. In the recent progress of polymer community, side chains are act as a crucial component in the design of novel conjugated polymers. They not only directly relate to the solubility but also affect the molecular packing motifs and thin film morphologies. The goal of this thesis is to address the effect of conjugated or alkyl side chain structures on the polymer thin film morphologies and the optoelectronic properties. In addition, the field-effect mobilities, photovoltaic, or memory characteristics are also probed to investigate the side chain engineering design on polymeric semiconductors for optoelectronic devices systematically. Three different strategies are explored in this thesis, as shown in followings: 1. Syntheses of two-dimensional branched thiophene extended octithiophene‐based conjugated polymers for field-effect transistors and photovoltaic cells: In Chapter 2, three octithiophene (8T)-based conjugated copolymers, including P8TSe, P8TT, and P8TTT, have been synthesized. The larger atomic radius selenium (Se) atom possesses higher polarizability than sulfur (T), inducing stronger intermolecular interactions in solid state. Also, 8T moiety could significantly lower the HOMO level and lead to the enhanced open circuit voltage because of its branched conformation. The hole mobilities of these 8T-based copolymers were in the range of 1.32×10-5 to 5.00×10-5 cm2V-1s-1 with on/off ratio of 104. Among them, P8TTT showed better characteristics than the other polymers due to the fused-ring TT can promote self-organization and minimize the steric interactions. The power conversion efficiencies (PCE) of the copolymers/PC71BM based photovoltaic cells were in the range of 1.28 - 2.30% under the illumination of AM 1.5G (100 mW cm-2). In particular, P8TTT showed the best PCE of 2.81%, as the blend films are prepared from the mixed solvent of o-dichlorobenzene (DCB) and 1,8-diiodoctane (DIO) (DCB/DIO = 97%:3% by volume). In Chapter 3, the synthesis, morphology and optoelectronic device applications of 2D extended quaterthiophene (4T)- and octithiophene (8T)-vinylene conjugated polymers, P4TV and P8TV, were explored. P4TV and P8TV exhibited smaller energy band gaps of 1.69 and 1.78 eV than that of parent polythiophenes, respectively, due to the reduced conformation distortion by the vinylene linkage. The highest field-effect hole mobilities of P4TV and P8TV were 0.12 and 0.0018 cm2V-1s-1, respectively, with on/off ratios around 104-105. In addition, the power conversion efficiency (PCE) of the P4TV/PC71BM based photovoltaic cells under the illumination of AM 1.5G (100 mW cm-2) was 4.04 %, which was significantly higher than that of P8TV/PC71BM with 2.69 %, due to its superior charge transport ability. However, P8TV had a better environmental stability attributed to its low-lying HOMO energy level. 2. Syntheses of main chain donor tethered side chain phenanthro[9,10-d]imidazole acceptor conjugated polymers for high performance flexible resistive memory devices: In Chapter 4, a bipolar-recorded resistive memory device consisting of a single-layer donor-acceptor conjugated polymer fabricated on plastic polyethylene naphthalate (PEN) have been developed. The newly designed conjugated polymer with a main-chain donor of fluorene and thiophene and a side-chain acceptor of phenanthro[9,10-d]-imidazole (PFT-PI) was synthesized as an active memory material. The reproducible, nonvolatile flash switching characteristics of each sandwiched PEN/Al/PFT-PI/Al memory device was demonstrated under bending. The flexible nonvolatile resistor memory devices with low threshold voltages (±2 V), low switching powers ( 100 μW cm−2), large ON/OFF memory windows (104), good retention (>104 s) and excellent endurance against electric and mechanical stimulus. The simple and facile device fabrication was obtained from a single PFT-PI memory material, without using charge injection layers or a complex multilayer structure. In Chapter 5, the synthesis and resistive memory device characteristics of new donor-acceptor conjugated poly(arylene vinylene), PVC-PI, PVT-PI, and PVTPA-PI, have been explored. The studied polymers possess similar HOMO energy levels (-5.08 ~ -5.18 eV), but with different LUMO energy levels (-2.24, -3.40, and -2.60 eV for PVC-PI, PVT-PI, and PVTPA-PI, respectively). The PVC-PI flexible memory with the sandwich configuration of PEN/Al/polymer/Al reveals the volatile static random access memory (SRAM) characteristic while the PVTPA-PI device exhibits the nonvolatile write-once-read-many-times (WORM) switching behavior. The above two devices could operate at low voltages (less than 2.5 V) with high ON/OFF current ratios (over 104) and exhibit excellent durability upon repeated bending tests. The PVT-PI device, however, only shows a diode-like electrical behavior. The polymer conformation affects the strength of D-A electrical polarization and charge trapping ability, leading to the variation on the volatility of the memory devices. 3. Effects of alkyl side chain design on charge transport: Synthesis, morphology, and stretchable transistor applications: In Chapter 6, three polymers with variant alkyl side chain structures (i.e. short linear, long linear, and branched alkyl side chains), namely P3HT, PTDPPTFT4, and PII2T, are evaluated for stretchable field-effect transistors. In addition, a facile method to efficiently identify suitable semiconducting polymers for organic stretchable transistors using soft contact lamination is described. In this method, the various polymers investigated are first transferred on elastomeric poly(dimethylsiloxane) (PDMS) slab, and subsequently stretched (up to 100 %) along with the PDMS. The polymer/PDMS matrix is then laminated on source/drain electrode-deposited Si substrates equipped with a PDMS dielectric layer. The polymer semiconductors can be repeatedly interrogated with laminate/delaminate cycles under different amounts of tensile strain, and the strain limitation of semiconductors enable different side chain structures can be derived. In Chapter 7, a series of isoindigo-based conjugated polymers (PII2F-CmSi, m=3-11) with alkyl siloxane-terminated side chains have been prepared, in which the branching point is systematically “moved away” from the conjugated backbone by one carbon atom. All soluble PII2F-CmSi (m=5-11) polymers exhibited hole charge carrier mobilities over 1 cm2V-1s-1, while the reference polymer with the same polymer backbone showed a much lower mobility of 0.13 cm2V-1s-1. PII2F-C9Si showed the highest mobility of 4.76 cm2V-1s-1, even though PII2F-C11Si exhibited the smallest π-π stacking distance at 3.379 Å. We concluded that it is beneficial that the branching site was further away from conjugated backbones to improve charge transport characteristics. The above studies demonstrate that the optoelectronic properties, charge carrier transport ability, solar cell efficiency, and memory behaviors can be manipulated using side chain engineering design. The device performances were tuned by controlling the chemical structures of conjugated side chains. Moreover, with variant alkyl side chain structures, the charge carrier mobility in stretched polymer thin films were changed, indicating the design of side chain on polymeric semiconductors plays a crucial role for next-generation electronic device application.
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Chien, Shang-Chieh, and 簡上傑. "Functional Polymer Blends for Optoelectronic Applications: Morphology, Fabrication and Device Engineering." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/55959790724715985777.
Full textAbstract:
博士國立交通大學
光電工程學系
100
Polymer optoelectronics fabricated through solution-processable methods commonly adopts polymer blends as the photoactive layer for improving their device performance. This dissertation proposed a series of functional polymer blends for various opto-electronical applications. The first part of this dissertation is to conceptually introduce a simple approach to realize nano-scaled interfacial modification for organic photovoltaic devices (OPVs). Through spontaneous vertical-phase-separation, a self-assembled poly(ethylene glycol) (PEG) buffer layer can be formed on the top-surface of the active layer, thereby naturally acting as a cathode buffer layer. The stable PEG materials can replace traditionally low-work-function metals, such as calcium (Ca), to improve the device stability. Furthermore, a series of systematical studies aiming for understanding the mechanism behind the formation of such self-assembled polymer buffer layer were performed from both thermodynamics and kinetics point of views. We found out that the surface energy of the substrate and the molecule weight of PEGs play essential roles in triggering the vertical-type morphological change. Moreover, not only for OPVs devices, this approach can also be employed to fabricate high-performance sky-blue, red and white polymer light-emitting diodes (PLEDs). The operating-voltage and the power efficiency have been improved after incorporating PEG. More importantly, we found that the charge-trapping effect lead to different enhancement mechanism between these PLEDs emitting different colors after the addition of PEG. Typical photoactive layer of polymer solar cells commonly consisted of one p-type conjugated polymer as the electron donor and one n-type electron acceptor. We additionally blended one functional fullerene derivatives, 1,2-dihydromethano-phenyl-C61-butyric acid methyl (Methano-PCBM), featuring a higher lowest unoccupied molecular orbital (LUMO) respect to that of PCBM, into the photoactive layer. Incorporating this Methano-PCBM, a larger energy offset between the highest occupied molecular orbital (HOMO) of the polymer donor and the LUMO of the acceptor can increase the open-circuit voltage (Voc); the resulting cascade energy level structure possibly also facilitated the charge transport in the devices. Further manipulation of this optimized photoactive layer could be employed to demonstrate efficient semi-transparent OPVs exhibiting high transparency. Finally, high-performance organic photodetectors featuring photomultiple effect have been demonstrated. The incorporation of near-infrared dyes not only resulted in electron-trapping behavior but their absorption was also optically complemented to the original film. As a result, high external quantum efficiencies (>7000%), high responsivities (32.4 A/W) and broadband response (300 nm to 1050 nm) have been achieved simtaneously at an extremely low operating voltage (–1.5 V).
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Chih-YuanChen and 陳志源. "Study on MOCVD grown Gallium Oxide film for Optoelectronic Device Applications." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/40517571201474039421.
Full textAbstract:
碩士國立成功大學
光電科學與工程學系
100
This thesis focuses on growth of gallium oxide epitaxial film used metal organic chemical vapor deposition technology. Deposited on c-plane (0001) sapphire.I use a different growth conditions to discuss the impact on the quality of gallium oxide films. Changing the deposition temperature、chamber pressure, and oxygen flow to study the influence of the epitaxial film quality,try to choose a better growth parameters.After analysis, the optimized parameters: chamber pressure 15Torr、Oxygen flow 200 standard cubic centimeter per minute (sccm)，Process temperature 500℃. Then a metal-semiconductor-metal solar-blind deep ultraviolet photodetector was fabricated on the β-Ga2O3 epilayer. The epilayer was grown on (0001) sapphire substrate using modified Emcore D180 MOCVD system.The metal organic source is TEGa, chemical reaction gas is oxygen. The as-grown β-Ga2O3 epilayer was annealed at 800 ºC in atmosphere or Oxygen or Nitrogen. Influence of surface states and point defects of β-Ga2O3 epilayers before and after N2 annealing are studied using room-temperature Photoluminescence (PL) and HR-XRD.We have shown that annealing single-crystalline β-Ga2O3 epilayer in Nitrogen atmosphere at 800 ºC can heal its surface states and point defects without disturbing crystal structure and quality.It also can improve the MSM photodetector performance of dark current and responsivity.
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Murali, Krishna. "Engineering van der Waals Heterojunctions for Electronic and Optoelectronic Device Applications." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4778.
Full textAbstract:
Efficient preparation and characterization of layered materials and their van der Waals
heterojunctions lay the foundation for various opportunities in both fundamental studies
and device applications. The vast library of 2D materials displays a range of electronic
properties, including conductors, semiconductors, insulators, semimetal, and superconductors, and shows strong light-matter interaction. The fact that each layer in the layered
material is bonded via van der Waals interaction opens up the possibility of assembling
different layers arbitrarily without any consideration over the precision of lattice match-
ing. This unique stacking with one-atomic-plane precision can unfold diverse van der
Waals heterostructure devices by efficiently engineering its energy band alignment. This
paves a path to design novel devices such as solar cells, photodetectors, light-emitting
diodes and transistors.
In this thesis, our motivation is to explore the electronic and optoelectronic characteristics of 2D materials and their heterojunctions. We focus on designing 2D heterostructures for the multi-functional devices including electronic (diode/transistor)
and optoelectronic (highly sensitive photodetection) applications. As the initial step, we
realized SnSe2 based photoconductor which shows a very high responsivity of 10^3 A/W
at 1 mV voltage bias. We investigated the role of trap states present at the channel-
substrate interface on the observed gain mechanism in typical planar 2D photoconductors.
Next, in order to improve the speed for a photodetector, we designed a heterostructure composed of ITO/WSe2/SnSe2 vertical heterojunction. This novel design helped us to achieve a large responsivity at near IR region while maintaining high operational speed. We achieved a high responsivity of more than 1100 A/W and fast transient response time in the order of 10 us. Considering the interest of broad band detection, we then fabricated a graphene-absorption-based photodetector where graphene can act as
the absorbing medium, utilizing its zero-band gap nature. The absorbed photo-carriers
are vertically transported in a fast time scale to a floating MoS2 quantum well, providing photo-gating. This structure exhibited the responsivity of 4.4 * 10^6 A/W at 30 fW
incident power which is higher than that of any reported graphene absorption-based photodetectors. As a continuation of the study of heterostructure transport characteristics,
we realized a backward diode with WSe2/SnSe2 structure which exhibits an ultra-high reverse recti cation ratio of 2.1 *10^4 with an impressive curvature coefficient of 37 V^(-1).
Finally, we proposed a novel methodology for the extraction of Schottky Barrier Height
(SBH) using a vertical heterojunction of multilayer transition metal dichalcogenide with
asymmetric contacts which allow easy and direct quantitative evaluation of SBH for two
contacts simultaneously.Visvesvarayya PhD Scheme
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Joyce, Hannah Jane. "Growth and characterisation of III-V semiconductor nanowires for optoelectronic device applications." Phd thesis, 2009. http://hdl.handle.net/1885/147722.
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Wang, Chih-Feng, and 王誌鋒. "Thienopyrazine-based Donor-Acceptor Conjugated Polymers : Synthesis, Properties, and Optoelectronic Device Applications." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/29567520057371582908.
Full textAbstract:
碩士國立臺灣大學
化學工程學研究所
96
Donor-acceptor conjugated polymers have been widely investigated in recent years. By optimization of donor and acceptor structures, the conjugated copolymers can exhibit broad absorption from visible region to near-infrared range for electronic and optoelectronic applications, such as light-emitting diodes, photovoltaic cells, and thin film transistor. However, the electronic and optoelectronic properties of thienopyrazine-based conjugated polymers have not been fully explored yet. The goal of this thesis is to investigate the effects of donor-acceptor or donor-acceptor-donor structures on the electronic properties of thienopyrazine based conjugated polymers. In chapter 2, the optical, electrochemical, and field effect charge transport properties of the new thienopyrazine-based alternating donor-acceptor conjugated copolymers were explored. The new copolymers, Poly[5-(2,5-bis(decyloxy)phenyl)-2,3- bis(4-(2-ethylhexyloxy)phenyl)thieno[3,4-b]pyrazine] (PDPTP), Poly[5-(9,9-dioctyl- 9H-fluoren-2-yl)-2,3-bis(4-(2-ethylhexyloxy)phenyl)thieno[3,4-b]pyrazine] (PFPTP), Poly[5-(9-(2-ethylhexyl)-9H-carbazol-3-yl)-2,3-bis(4-(2-ethylhexyloxy)phenyl)thieno[3,4-b]pyrazine] (PCPTP) and Poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-5-(thiophen-2-yl) thieno[3,4-b]pyrazine] (PTPTP) had excellent solubility and broad optical absorption bands with absorption maxima at 540-950nm in thin film. The PTPTP exhibits the smallest band gap (0.98eV), indicating a stronger intramolecular charge transfer. The four polymers show the low ionization potentials (4.57-4.99 eV) and high electron affinity (3.26-3.49eV). The hole mobilities of PDPTP, PCPTP, and PTPTP are 2.62×10-6, 2.74×10-5, and 2.00×10-4 cm2V-1s-1. PTPTP has the highest hole mobility due to low band gap and strong intramolecular charge transfer.The AFM topographic images of the copolymers show smooth and amorphous phases. From these results, intramolecular charge transfer might be main impact on hole mobility. In chapter 3, thienopyrazine-based donor-acceptor-donor alternating conjugated copolymers were synthesized. The copolymers including Poly[5-(5-(2,5-bis(decyloxy)-4-methylphenyl)thiophen-2-yl)-2,3-bis(4-(2-ethylhexyloxy)phenyl)-7-(5-methylthiophen-2-yl)thieno[3,4-b]pyrazine] (PDDTTP), Poly[5-(5-(9,9- dioctyl-9H-fluoren-2-yl)thiophen-2-yl)-2,3-bis(4-(2-ethylhexyloxy)phenyl)-7-(thiophen-2-yl)thieno[3,4-b]pyrazine] (PFDTTP), and Poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-5 ,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine] (PDTTP) exhibit broad optical absorption bands (662-816nm) and small optical band gaps (1.15-1.57eV). All polymers exhibit reversible oxidation and reduction and low ionization potential (4.62-4.98 eV). The hole mobility of PDDTTP, PFDTTP, and PDTTP are 7.24×10-4, 1.61×10-3 and 1.16×10-3cm2V-1s-1. The hole mobility of PFDTTP is the highest probably due to the relatively smooth and amorphous phase in thin film. According to these results, thienopyrazine-based donor-acceptor-donor copolymers combine small band gap and high carrier mobility. Such polymers may have potential optoelectronic device applications, such as thin film transistor and photovoltaic cells.
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Wang, Chih-Feng. "Thienopyrazine-based Donor-Acceptor Conjugated Polymers : Synthesis, Properties, and Optoelectronic Device Applications." 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-1407200815023600.
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Chang, Yuan-Ho, and 張源合. "Fabrication of Carbon-nitride Thin-Film by ECR-CVD for Optoelectronic Device Applications." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/68156078062746141474.
Full textAbstract:
碩士南台科技大學
電機工程系
94
Carbon-nitride is an interesting and important material owing to its several superior properties including high bulk modulus, high hardness, high decomposition temperature, high strength, high thermal conductivity and excellent resistance to corrosion and wear. However, crystalline carbon nitride (c-CN) is difficult to form, and hence its practical applications were greatly limited. The amorphous carbon-nitride (a-CN) thin-film deposited on silicon substrates is a highly functional wide-bandgap semiconductor material due to its similar material characteristics to c-CN. In addition, its optical bandgap is estimated to 4 eV above, making it a suitable candidate for development of short-wavelength or broad-band optoelectronic devices. In this thesis, a-CN thin-films were deposited on different substrates by an electron-cyclotron-resonant-chemical-vapor-deposition (ECR-CVD) technique. Properties of as-deposited films were adjusted by different microwave power and gas compositional ratios and were characterized by SEM, AFM, XRD, AES, UV/Visible Spectrophotometer and Raman Spectrophotometer. Experimental results showed that optical band-gaps of a-CN thin-films decreased with increasing microwave power or decreasing compositional ratio of nitrogen in the precursor. It is supposed that lower optical bandgaps were resulted from larger nitrogen-to-carbon ratios (N/C ratios) of films. Higher microwave power induced more intense plasma energy and more decomposition of nitrogen gas, thus making larger N/C ratios and lower optical bandgaps. On the contrary, if the proportion of nitrogen gas in the precursor increased, the plasma density reduced, thus leading to a smaller N/C ratio and a higher optical bandgap. In conclusion, a-CN thin-films with adjustable optical bandgaps can be deposited by ECR-CVD. It indicated this novel material have great potential for applications in optoelectronic devices.
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Kang, Jung-Hyun. "Epitaxial growth and characterisation of GaAs nanowires on Si for optoelectronic device applications." Phd thesis, 2012. http://hdl.handle.net/1885/149685.
Full textAbstract:
This thesis examines the Au-assisted growth of GaAs nanowires by MOCVD, and how this growth process can be tailored to produce well-aligned nanowires on Si suitable for applications in electronics and optoelectronics. i) Improving the morphology of GaAs nanowires on Si: Straight, vertically aligned GaAs nanowires were grown on Si (111) substrates coated with thin GaAs buffer layers. V/III precursor ratio and growth temperature are crucial factors influencing the morphology and quality of buffer layers. A double layer structure, consisting of a thin initial layer grown at low V/III ratio and low temperature, followed by a layer grown at high V/III ratio and high temperature, was crucial for achieving straight, vertically aligned GaAs nanowires on Si (111) substrates. An in-situ annealing step at high temperature after buffer layer growth improved the surface and structural properties of the buffer layer, which further improved the morphology of GaAs nanowire growth. ii) Improving the crystal structure of GaAs nanowires on Si: Defect-free GaAs nanowires were grown on Si by using either a two-temperature growth mode consisting of a short initial nucleation step under higher temperature followed by subsequent growth under lower temperature or a rapid growth rate mode with high source flow rate. These two growth modes not only eliminated planar crystallographic defects but also significantly reduced tapering. Core-shell GaAs-AlGaAs nanowires grown by two-temperature growth mode showed improved optical properties with strong photoluminescence and long carrier life times. iii) Optimizing the growth conditions for perfect GaAs nanowires on Si: By systematically manipulating the arsine (group-V) and triethylgallium (group-III) precursor flow rates, it was found that TMGa flow rate has the most significant effect on nanowire quality. Defect-free GaAs nanowires with minimal tapering and long exciton lifetimes were obtained at the highest TMGa flow rates. It was observed that Ga adatom concentration significantly affacts the growth of GaAs nanowires. iv) Band-gap engineering for GaAs nanowires on Si: Based on the defect-free GaAs nanowires grown by the two-temperature growth mode, highly strained core-shell nanowires of excellent optical quality were grown with GaAs cores and GaP shells. Photoluminescence from these nanowires was observed at energies dramatically blue-shifted from the unstrained GaAs free exciton emission energy. Using Raman scattering, it was possible to separately measure the degree of compressive and shear strain of the GaAs core and the Raman response of the GaP shell was related to tensile strain. This work presents significant advances in the growth of exceptionally high quality GaAs nanowires on Si, and reveals intriguing behaviour in the growth of nanoscale materials. These findings will greatly assist the development of future GaAs nanowire-based electronic and optoelectronic devices, and are expected to be more broadly relevant to the rational synthesis of other III-V nanowire materials on Si substrate and ultimate integration of III-V semiconductor optoelectronics and Si based microelectronics. -- provided by Candidate.
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Ramesh, Vidya. "Growth and characterisation of InP-based core-shell nanowires for optoelectronic device applications." Master's thesis, 2011. http://hdl.handle.net/1885/149902.
Full textAbstract:
In order to achieve high performance III-V nanowire heterostructure based devices, it is essential that the heterostructures are of good structural and optical quality. Hence controlling the morphology and crystal structure is a critical factor in the nanowire heterostructure growth. Au-nanoparticle assisted vapour-liquid-solid (V-L-S) technique is one of the superior methods used in recent years for nanowire growth.
This thesis investigates InP-based core-shell nanowire growth by the metal organic chemical vapour deposition (MOCVD) on (111)B InP substrates via V-L-S growth mechanism. The microstructure of core-shell nanowires is characterised by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Micro-photoluminescence and micro-Raman measurements are carried out to study the optical properties.
The growth of InP/In
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Jiang, Nian. "Growth and Characterisation of GaAs/AlGaAs Core-shell Nanowires for Optoelectronic Device Applications." Phd thesis, 2015. http://hdl.handle.net/1885/104572.
Full textAbstract:
III-V semiconductor nanowires have been investigated as key
components for future electronic and optoelectronic devices and
systems due to their direct band gap and high electron mobility.
Amongst the III-V semiconductors, the planar GaAs material system
has been extensively studied and used in industries. Accordingly,
GaAs nanowires are the prime candidates for nano-scale devices.
However, the electronic performance of GaAs nanowires has yet to
match that of state-of-the-art planar GaAs devices. The present
deficiency of GaAs nanowires is typically attributed to the large
surface-to- volume ratio and the tendency for non-radiative
recombination centres to form at the surface. The favoured
solution of this problem is by coating GaAs nanowires with AlGaAs
shells, which replaces the GaAs surface with GaAs/AlGaAs
interface.
This thesis presents a systematic study of GaAs/AlGaAs core-shell
nanowires grown by metal organic chemical vapour deposition
(MOCVD), including understanding the growth, and characterisation
of their structural and optical properties. The structures of the
nanowires were mainly studied by scanning electron microscopy and
transmis- sion electron microscopy (TEM). A procedure of
microtomy was developed to prepare the cross-sectional samples
for the TEM studies. The optical properties were charac- terised
by photoluminescence (PL) spectroscopy. Carrier lifetimes were
measured by time-resolved PL. The growth of AlGaAs shell was
optimised to obtain the best optical properties, e.g. the
strongest PL emission and the longest minority carrier
lifetimes.
The sidewalls of the vapour-liquid-solid (VLS) grown GaAs
nanowires were investi- gated. It was found that a Reuleaux
triangle with 3 {112}A curved surfaces is the actual shape of the
nanowire at the growth interface. This Reuleaux triangle changes
into well defined {112} facets as a result of the simultaneous
radial growth. A theoretical model was developed to explain the
orientations of nanowire sidewall facets.
The sidewalls of GaAs nanowires were found to transform to {110}
facets at high temperature as a result of surface atom migration.
The rate of the facet transformation was found to be controlled
by temperature and the difference in the surface energies, which
leads to different faceting behaviour along the length of the
nanowire. While the sidewalls of the top segment were fully
transformed into {110} facets, the sidewalls of the bottom of the
nanowires were a mixture of {110} and {112} facets. This
facet-change along the length of the nanowire directly affected
the subsequent growth of AlGaAs shell. This was relevant to the
non-uniform PL emission and the minority carrier lifetimes (tmc)
along the GaAs/AlGaAs core-shell nanowires. The strongest PL
emission and longest tmc was observed where the GaAs core had six
{110} facets. PL intensity and tmc decreased towards the bottom
of the nanowire where the sidewall facets of the GaAs core
consisted of both {110} and {112} facets.
The effect of AlGaAs shell growth parameters (including V/III
ratio, temperature and time) on the optical properties of
GaAs/AlGaAs core-shell nanowires was investigated on nanowires
catalysed by Au particles with a diameter of 50 nm. The V/III
ratio and shell growth temperature were found to profoundly
affect the optical properties. A high V/III ratio and/or a high
growth temperature dramatically increased tmc. Further increasing
the V/III ratio and/or growth temperature resulted in drop of
tmc. Interme- diate V/III ratio and shell growth temperature were
chosen as a compromise to achieve long tPL. The AlGaAs shell
growth time also showed a significant effect on tmc. tmc
increased with shell growth time to a maximum, followed by a
further drop with longer shell growth time. With the optimised
AlGaAs shell growth, an average carrier life- time of (1.02 ±
0.4) ns was achieved from single GaAs/AlGaAs core-shell nanowires
at room temperature. This is comparable to self-assisted
nanowires grown by molec- ular beam epitaxy and also proved that
Au catalyst is not detrimental to the optical properties in
VLS-grown GaAs nanowires. The long lifetimes are mainly
attributed to the improvement of the GaAs/AlGaAs interface
quality that is comparable with planar heterostructures.
The effect of AlGaAs shell growth time and shell thickness on tPL
were investigated. It was found that both the shell thickness and
shell growth time affected tmc. A certain shell thickness is
required to prevent the carriers generated in GaAs core from
tunnelling through the AlGaAs shell and recombining at the free
surface of GaAs cap layer. Beyond this thickness, the shell
growth time, which is related to the diffusion at the
heterointer- face, becomes the primary parameter controlling the
carrier lifetimes. Lifetimes as long as 1.9 ns were achieved by
reducing the effect of diffusion.
This work presents an in-depth understanding of the geometry of
GaAs nanowires, demonstrates GaAs/AlGaAs core-shell nanowires
with optical quality comparable with planar heterostructures and
reveals intriguing structural/optical behaviour of the nano-
wires. These findings will greatly assist the fabrication of
efficient nanowire devices and show a strong future for
nano-optoelectronic devices based on nanowires.
43
Bhardwaj, Devanshi. "Vanadium Dioxide: Bulk and Thin Films for Device Applications." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4758.
Full textAbstract:
In the present era, energy consumption is more than the energy that is generated for which renewable as well as non-renewable sources are used. In order overcome this lag, researchers are developing smart materials (thermochromic smart window and metamaterial) where energy generation is enough to deal with the energy demand in order to have a better efficiency. Vanadium dioxide (VO2) is a transition metal oxide which is extensively studied for smart window and metamaterial applications. It undergoes a first-order phase (semiconductor to metal) transition at 68 degC (TSMT). During the transition, a change in resistance as well reflectance (IR region) is observed. Due to the complexity in the synthesis, achieving phase pure VO2 is difficult. Earlier in the group, VO2 powders has been synthesised using Solution Combustion Synthesis (SCS) and thin films using Ultrasonic Nebulised Spray Pyrolysis of Aqueous Combustion Mixture (UNPSACM) and CVD. W and Mo was doped in VO2 where the TSMT was reduced to 25 degC with 2 at. % of W dopant. But upon doping, only 40 % of visible transparency was observed, thereby making VO2 unsuitable for smart window application. Further, the thin films showed the roughness value of 0.2 micron-m and 18 nm with UNSPACM and CVD respectively, making VO2 unsuitable for optical applications.
In this study, we report the effect of scandium doping on bulk (by SCS) and thin films (by UNSPACM) on SMT and optical characteristics of VO2 to use it for smart window applications. We observed that Sc doping induced the blue-shift in the optical spectrum without showing any change in the transition temperature (TSMT).
Different synthesis techniques like DC Reactive Sputtering and Pulsed Laser Deposition (PLD) were explored for getting optimized condition to achieve phase pure VO2 in single-step and reducing the roughness of vanadium dioxide thin films for smart window and metamaterial application. DC Reactive Sputtering was found to be a two-step synthesis process to achieve phase pure VO2. The roughness was found to be 9.8 nm which was less than that observed earlier in the group.
PLD was further explored, where it was found to be one-step synthesis process to get phase pure VO2 and roughness value was reduced to 3.8 nm. Based on the best conditions observed, photodetection measurements were done on thin films which showed promising results with that reported in the literature.
44
"Sensors and Their Applications for Connected Health and Environment." Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.51613.
Full textAbstract:
abstract: Connected health is an emerging field of science and medicine that enables the collection and integration of personal biometrics and environment, contributing to more precise and accurate assessment of the person’s state. It has been proven to help to establish wellbeing as well as prevent, diagnose, and determine the prognosis of chronic diseases. The development of sensing devices for connected health is challenging because devices used in the field of medicine need to meet not only selectivity and sensitivity of detection, but also robustness and performance under hash usage conditions, typically by non-experts in analysis. In this work, the properties and fabrication process of sensors built for sensing devices capable of detection of a biomarker as well as pollutant levels in the environment are discussed. These sensing devices have been developed and perfected with the aim of overcoming the aforementioned challenges and contributing to the evolving connected health field. In the first part of this work, a wireless, solid-state, portable, and continuous ammonia (NH3) gas sensing device is introduced. This device determines the concentration of NH3 contained in a biological sample within five seconds and can wirelessly transmit data to other Bluetooth enabled devices. In this second part of the work, the use of a thermal-based flow meter to assess exhalation rate is evaluated. For this purpose, a mobile device named here mobile indirect calorimeter (MIC) was designed and used to measure resting metabolic rate (RMR) from subjects, which relies on the measure of O2 consumption rate (VO2) and CO2 generation rate (VCO2), and compared to a practical reference method in hospital. In the third part of the work, the sensing selectivity, stability and sensitivity of an aged molecularly imprinted polymer (MIP) selective to the adsorption of hydrocarbons were studied. The optimized material was integrated in tuning fork sensors to detect environmental hydrocarbons, and demonstrated the needed stability for field testing. Finally, the hydrocarbon sensing device was used in conjunction with a MIC to explore potential connections between hydrocarbon exposure level and resting metabolic rate of individuals. Both the hydrocarbon sensing device and the metabolic rate device were under field testing. The correlation between the hydrocarbons and the resting metabolic rate were investigated.Dissertation/Thesis
Doctoral Dissertation Chemical Engineering 2018
45
NAGPAL, DIVYANSHI, and TANISHA BHADAURIA. "STRUCTURAL AND SPECTROSCOPIC STUDIES OF Eu3+ ACTIVATED POTASSIUM BISMUTH MOLYBDATE PHOSPHOR FOR OPTOELECTRONIC DEVICE APPLICATIONS." Thesis, 2022. http://dspace.dtu.ac.in:8080/jspui/handle/repository/19491.
Full textAbstract:
Red emitting Eu3+ activated K5BiMo4O16 (KBM: Eu3+) phosphor has been synthesized via high
temperature solid state reaction route and explored via investigating various structural and spectroscopic
properties. The phase purity of the as-synthesized KBM samples have been analysed through X-ray
diffraction technique. Morphological properties have been analysed through SEM images and the
vibration modes have been identified in KBM crystal using Fourier Transform Infrared (FT-IR)
spectroscopy. The luminescence spectrum of KBM: Eu3+ phosphor indicates the characteristic peaks of
Eu3+ positioned at 578, 588, 612, 657 and 704 nm under 392 and 464 nm excitation wavelength. The color
coordinates of KBM: Eu3+ phosphor excited with 392 and 464 nm wavelength are (0.657, 0.342) and
(0.655, 0.344) located in red region. Based on the above-mentioned characteristics, KBM: Eu3+ phosphor
may be a potential candidate to utilize in optoelectronic applications such wLEDs and solar cells.
46
Chih-ChiangYang and 楊智強. "Metal-Modified ZnO Nanostructures Grown by Low-Temperature Hydrothermal Method for Optoelectronic Device Applications." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/4wt2f6.
Full textAbstract:
博士國立成功大學
微電子工程研究所
104
In this dissertation, the metal-modified ZnO nanostructures were grown on an a-ZnO seed layer via the low-temperature hydrothermal method (90 °C) and applied to metal semiconductor-metal (MSM) ultraviolet (UV) photodetector (PD) and field emission devices. This dissertation is divided into three parts. In the first part, Ga-doped ZnO nanosheet-based (MSM) ultraviolet (UV) photodetectors are investigated and Ga-doped ZnO nanorods (NRs) with different Ga concentrations are synthesized for application to an MSM UV PD. In the second part, the synthesis of Ag nanoparticle (NP)-decorated ZnO NR MSM UV PDs is discussed. Finally, the third part discusses the synthesis of Ag NP-decorated ZnO NR field emitters under UV illumination. The beginning of this dissertation is divided into two sections. First, vertical Ga-doped ZnO nanosheets are synthesized on a ZnO-seeded glass substrate via the hydrothermal method at low temperature and used to fabricate a GZO NS MSM UV PD. The average length and average diameter of the interwoven GZO nanosheet was 720 and 26 nm. The measured cutoff wavelength of the PDs was 340 nm when biased at 1 V, and the measured fabricated PD responsivity was 2.85 × 10-5. The corresponding UV-to-visible rejection ratio was approximately 81 when biased at 1 V. The noise equivalent power (NEP) of the fabricated GZO NS MSM PD was 5.92 × 10-9 W, and its specific detectivity was 2.24 × 109 cm • Hz0.5 • W-1. The fabrication of ZnO NRs doped with various Ga concentrations on a ZnO-seed layer/glass substrate via the low temperature hydrothermal method is then presented. Ga-doped ZnO (GZO) NR-based UV PDs were fabricated under a bias of 1 V. The measured device responsitivities of the ZnO NRs doped with 0.25, 0.5, and 1 mM Ga were 2.2 × 10−2, 14.9, and 14.1 A/W, respectively. Varying the Ga concentration allowed control of the responsivity of the fabricated PDs. Under a bandwidth of 1 kHz and applied bias of 1 V, the NEP of the GZO NR PDs with 0.25, 0.5, and 1 mM Ga were 1.06 × 10−9, 3.13 × 10−11, and 1.29 × 10−10 W, respectively, and their corresponding detectivities were 1.24 × 1010, 4.21 × 1011 W, and 1.01 × 1011 cm•Hz0.5•W−1. In the second part of this dissertation, Ag NP-decorated ZnO NR arrays were synthesized on a ZnO-seeded glass substrate using a novel and simple hydrothermal method. Under an applied bias of 0.2 V and incident light wavelength of 380 nm, a UV PD based on the Ag NP-decorated ZnO NRs showed a high responsivity of 12.4 A W with a corresponding UV-to-visible rejection ratio of 4478. The noise spectrum of the UV PD was obtained using pure 1/f noise, and the NEP of the fabricated Ag NP-decorated ZnO NR MSM PD was found to be 4.85 × 10−11 W; a detectivity of 2.72 × 1011 cm·Hz0.5·W−1 was also observed. Finally, Ag NP-decorated ZnO NRs were successfully synthesized on a glass substrate via the hydrothermal method at a low temperature of 90 °C and used to fabricate Ag NP-decorated ZnO NR field emission devices. The resulting Ag NP-decorated ZnO NRs of ultra-turn-on field was reduced to approximately 3.93 and 2.04 V/μm in the dark and under UV illumination, respectively, and the corresponding field enhancement factors were 1,593 and 57,872. These results indicate that the enhanced FE of Ag NP-decorated ZnO NRs can be attributed to the effective formation of potential wells on the surfaces of the Ag NPs, which collect electrons by field emission from the Ag NPs to the vacuum level to enhance field emission.
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Wu, Fan-Lei, and 吳凡磊. "Technologies of Epitaxial Lift-Off Process and Reused GaAs Substrate for Optoelectronic Device Applications." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/40568191288014695026.
Full textAbstract:
博士國立中興大學
精密工程學系所
104
In this dissertation, two important techniques were respectively demonstrated for the development of optoelectronic devices. In the first part, the characteristics of different etching solutions applied to the epitaxial lift-off process (ELO) for separating the epitaxial layer from GaAs substrate were explored in detail. These etching solutions included the hydrofluoric acid (HF) solution and the hydrophilic solutions, such as HF:acetone, HF:isopropanol, HF:methanol. In lateral etching the AlAs sacrificial layer, the mixed solutions all displayed higher lateral etching rates ranging between 7.4 and 14.3 μm/min than pure HF solution (3.6 μm/min). Among these mixed solutions, although the HF:acetone solution had medium surface tension and contact angle, it was still exhibited the highest lateral etching rate (14.3 μm/min). Additionally, it was worthy to note that the sample surface had few by-products as compared with other solutions while using HF:acetone solution. This indicated that the reaction bubble vent possessed few obstacles during the etching reaction for avoiding reducing the reaction rate. Furthermore, it was found that using HF:acetone solution nearly prevented from degradation of the cell efficiency after the ELO process. As concerning the reuse times of GaAs substrate, indium and phosphorous can remain on the reused GaAs substrate surface via diffusing from the epilayers. These residues can result in the degradation of subsequent epilayer quality. An additional wet etching process, which used NH4OH:H2O2:H2O2, can not only remove the residues but also decrease the surface roughness of reused GaAs substrate. Moreover, the surface roughness of reused GaAs substrate can be further improved by annealing at 650oC in arsine and hydrogen atmosphere with 30 minutes. A GaAs-based solar cell was successfully achieved on the four-times reused GaAs substrate which was fabricated by ELO process and two optimized methods mentioned above. The efficiency of solar cell was enhanced to 1.68 times. It confirmed that the NH4OH:H2O2:H2O2 etching and annealing processes benefited to the reliability and reused times of GaAs substrate. For exploring the possibility of applying ELO process to LED devices (ELO-LED), the thin-film vertical-type AlGaInP LED on Cu substrate was fabricated by using ELO process to transfer the substrate from GaAs to Cu substrate. Cu substrates with various patterns were designed in order to prevent the crack formation in the epilayer during the ELO process. The stress distribution in the LED during the ELO process was simulated by the finite element method. The Cu substrate with an optimum pattern which can confine the maximum stress to the chip edges and significantly reduce stress process was obtained based on the simulation results. This Cu substrate could avoid generating cracks after separating the GaAs substrate. In addition, the chemical etching process was regularly used to remove the GaAs substrate and then transfer to Cu substrate in the LED device process (CE-LED). To compare the two different substrate removal methods (ELO-LED and CE-LED), the forward voltages (@350 mA) of the CE-LED and ELO-LED were 2.20 and 2.29 V, and the output powers (@350 mA) were 49.9 and 48.2 mW, respectively. Furthermore, the surface temperatures (@350 mA) of these two samples were 46.9-48.3 and 45.2-47.0oC, respectively. Obviously, the device characteristics of the ELO-LED were very similar to the CE-LED. It confirmed that the design of optimum patterned Cu substrate was very helpful to obtain the thin-film vertical-type AlGaInP LEDs. This also implied that the ELO technique can effectively be applied to the optoelectronic devices, reducing the cost. The second part in the thesis focused on the effect of various buffer layers on the efficiency of InGaAs solar cells. Three different buffer layers on solar cells including low-temperature buffer layer (2S-cell), step-graded layer (S-cell), and linear-graded layer (L-cell) were fabricated. Dislocation defects only obviously exited in these buffer layers by the transmission electron microscopy (TEM) observation. Therefore, these dislocation defects can significantly suppress the extension up to the active In0.16Ga0.84As layer. Furthermore, the In0.16Ga0.84As epilayer of L-cell exhibited the lowest defect density, residual stress, carrier recombination rate. The efficiency of the 2S-cell, S-cell and L-cell were 9.8%, 14.4%, 16.1%, respectively. Summarized above results, the L-cell of employing the InxGa1-xAs linear-graded buffer layer can achieve good epilayer quality and high cell efficiency. In addition, various angles ranging from 0° to 90° for the stripe-shaped front electrode were designed on the L-cell. When the front electrode angles were fixed at 0° and 90°, the devices possessed high conversion efficiencies of 16.34% and 16.58%, respectively. This was attributed to the change of the transport path of the carriers, inducing that the carriers can be avoided confining the dislocations.
48
"Pulsed Laser Deposition of Highly Conductive Transparent Ga-doped ZnO for Optoelectronic Device Applications." Doctoral diss., 2011. http://hdl.handle.net/2286/R.I.8868.
Full textAbstract:
abstract: Transparent conductive oxides (TCOs) are used as electrodes for a number of optoelectronic devices including solar cells. Because of its superior transparent and conductive properties, indium (In) tin (Sn) oxide (ITO) has long been at the forefront for TCO research activities and high-volume product applications. However, given the limited supply of In and potential toxicity of Sn-based compounds, attention has shifted to alternative TCOs like ZnO doped with group-III elements such as Ga and Al. Employing a variety of deposition techniques, many research groups are striving to achieve resistivities below 1E-4 ohm-cm with transmittance approaching the theoretical limit over a wide spectral range. In this work, Ga-doped ZnO is deposited using pulsed laser deposition (PLD). Material properties of the films are characterized using a number of techniques. For deposition in oxygen at pressures >1 mTorr, post-deposition annealing in forming gas (FG) is required to improve conductivity. At these higher oxygen pressures, thermodynamic analysis coupled with a study using the Hall effect measurements and photoluminescence spectroscopy suggest that conductivity is limited by oxygen-related acceptor-like defects in the grains that compensate donors, effectively reducing the net carrier concentration and creating scattering centers that reduce electron mobility. Oxygen is also responsible for further suppression of conductivity by forming insulative metal oxide regions at the grain edges and oxygen-related electron traps at the grain boundaries. The hydrogen component in the FG is thought to passivate the intra-grain acceptor-like defects and improve carrier transport across these grain boundaries. Given this deleterious effect of oxygen on conductivity, depositions are performed in pure argon (Ar), i.e., the only oxygen species in the growth ambient are those ejected directly from the PLD solid source target. Ga-doped ZnO deposited in Ar at 200 °C and 10 mTorr have resistivities of 1.8E-4 ohm-cm without the need for post deposition annealing. Average transmittance of the Ga-doped films is 93% over the visible and near infrared (IR) spectral regions, but free carrier absorption is a limiting factor further into the IR. After annealing in FG at 500 °C, a 300 nm Ar film has a Haacke figure of merit of 6.61E-2 sq. ohm.Dissertation/Thesis
Ph.D. Materials Science and Engineering 2011
49
"Material Properties of MBE Grown ZnTe, GaSb and Their Heterostructures for Optoelectronic Device Applications." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.15804.
Full textAbstract:
abstract: Recently a new materials platform consisting of semiconductors grown on GaSb and InAs substrates with lattice constants close to 6.1 A was proposed by our group for various electronic and optoelectronic applications. This materials platform consists of both II-VI (MgZnCdHg)(SeTe) and III-V (InGaAl)(AsSb) compound semiconductors, which have direct bandgaps spanning the entire energy spectrum from far-IR (~0 eV) up to UV (~3.4 eV). The broad range of bandgaps and material properties make it very attractive for a wide range of applications in optoelectronics, such as solar cells, laser diodes, light emitting diodes, and photodetectors. Moreover, this novel materials system potentially offers unlimited degrees of freedom for integration of electronic and optoelectronic devices onto a single substrate while keeping the best possible materials quality with very low densities of misfit dislocations. This capability is not achievable with any other known lattice-matched semiconductors on any available substrate. In the 6.1-A materials system, the semiconductors ZnTe and GaSb are almost perfectly lattice-matched with a lattice mismatch of only 0.13%. Correspondingly, it is expected that high quality ZnTe/GaSb and GaSb/ZnTe heterostructures can be achieved with very few dislocations generated during growth. To fulfill the task, their MBE growth and material properties are carefully investigated. High quality ZnTe layers grown on various III-V substrates and GaSb grown on ZnTe are successfully achieved using MBE. It is also noticed that ZnTe and GaSb have a type-I band-edge alignment with large band offsets (delta_Ec=0.934 eV, delta_Ev=0.6 eV), which provides strong confinement for both electrons and holes. Furthermore, a large difference in refractive index is found between ZnTe and GaSb (2.7 and 3.9, respectively, at 0.7 eV), leading to excellent optical confinement of the guided optical modes in planar semiconductor lasers or distributed Bragg reflectors (DBR) for vertical-cavity surface-emitting lasers. Therefore, GaSb/ZnTe double-heterostructure and ZnTe/GaSb DBR structure are suitable for use in light emitting devices. In this thesis work, experimental demonstration of these structures with excellent structural and optical properties is reported. During the exploration on the properties of various ZnTe heterostructures, it is found that residual tensile strains exist in the thick ZnTe epilayers when they are grown on GaAs, InP, InAs and GaSb substrates. The presence of tensile strains is due to the difference in thermal expansion coefficients between the epilayers and the substrates. The defect densities in these ZnTe layers become lower as the ZnTe layer thickness increases. Growth of high quality GaSb on ZnTe can be achieved using a temperature ramp during growth. The influence of temperature ramps with different ramping rates in the optical properties of GaSb layer is studied, and the samples grown with a temperature ramp from 360 to 470 C at a rate of 33 C/min show the narrowest bound exciton emission peak with a full width at half maximum of 15 meV. ZnTe/GaSb DBR structures show excellent reflectivity properties in the mid-infrared range. A peak reflectance of 99% with a wide stopband of 480 nm centered at 2.5 um is measured from a ZnTe/GaSb DBR sample of only 7 quarter-wavelength pairs.Dissertation/Thesis
Ph.D. Physics 2012
50
Lin, Yu-Hsiang, and 林裕翔. "Study of 2-D and 3-D Nanosphere Lithographyfor Optoelectronic Device and Sensor Applications." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/31610052764531936539.
Full textAbstract:
碩士臺灣大學
材料科學與工程學研究所
95
Nanosphere lithography (NSL) is a novel method for the fabrication of hexagonal close-packed structures by self-assembly monolayer nanosphere array on flat substrates. Here the monolayer nanospheres are taked as etching mask layer like patterned resists. Furthermore, the period and dimension can be controlled by the size of nanospheres. Because of cheap, rapid, and extensive applications, it’s one of the important nanofabrication techniques. In the fabrication of monolayer nanosphere array, we fabricate large-area monolayer nanospheres by spin coating method and using as etching mask for the fabrication of sub-wavelength pyramid anti-reflection structure on silicon substrate by wet etching and dry etching processes. And the reflectance of silicon substrates can be reduced to 3%. Besides, we fabricate periodical metal hole-arrays which have high surface plasma transmission by deposition and lift-off processes on monolayer nanospheres. And in three-dimensional (3D) opal-like photonic crystal, we investigate the influence of different environments and nanospheres with different surface charge distribution on opal structures. Besides, we provide a rapid fabrication method of fabricating silica inverse opal structure. And we try to infiltrate gold nanoparticles (Au NPs) into inverse opal. It’s hard to catch Au NPs in 3D nano structure without aggregation, but we find the optimal parameter to fabricate inverse opal structure with adhered Au NPs uniformly. This photonic crystal have both photonic band gap(PBG) and localized surface plasma resonance (LSPR) effects, and the two properties in one structure can be used to probe the refractive index of infiltrated solution and the properties of bio-molecular which adhered on Au NPs. At last, we use drop coating method to add organic luminescence material on opal and find the luminescence wavelength at photonic band gap is confined by opal structures. When the detector angle is changed, the confined luminescence wavelength of opal which added organic luminescence material is also changed. Besides, the emission intensity can be enhanced by energy transfer of polystyrene and large surface area.