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Dissertations / Theses on the topic 'Optoelectric properties'
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Altalebi, Hasanain Basim. "Processing of Ultra-Thin Film of Un Modified C60 Fullerene Using the Langmuir-Blodgett Technique. Effect of Structure on Stiffness and Optoelectric Properties." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1506520625022502.
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Gavranović, Stevan. "Monokrystaly perovskitů pro detekci elektromagnetického záření." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2021. http://www.nusl.cz/ntk/nusl-445139.
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This thesis is focused on the study of the detection of electromagnetic radiation using monocrystalline perovskites. Theoretical part deals with basic principles of detections and possible applications of hybrid perovskite crystals in the field of ultraviolet and visible spectrum detection. Parameters of the recently published perovskite photodetectors are also presented. Experimental part describes synthesis, structural and optical properties of MAPbBr3 single crystals and electrical characterization of the Au/MAPbBr3/Au photodetector. Photodetector parameters (responsivity, external quantum efficiency and specific detectivity) are calculated based on the spectral and switching (on/off) current responses.
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Ginger, David Stanton. "Optoelectronic properties of CdSe nanocrystals." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621187.
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Landes, Christy. "The dependence of the opto-electronic properties of CdSe nanoparticles on surface properties." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/30657.
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Figueiredo, José Maria Longras. "Optoelectronic properties of resonant tunnelling diodes." Tese, Universidade do Porto. Reitoria, 2000. http://hdl.handle.net/10216/14347.
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Casey, Abby. "Optoelectronic properties of new conjugated materials." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/46164.
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Next-generation electronic devices which are cheap, lightweight and flexible could be realised through the use of solution processable organic polymer and small molecule semiconductors. Unlike inorganic semiconductors such as silicon, soluble organic semiconductors could be processed using traditional high through-put printing techniques such as roll-to-roll processing and ink-jet printing, which would dramatically reduce manufacturing costs. Whilst organic semiconductors are not expected to be as high performance as inorganic semiconductors, improvements in performance are still required before commercialisation is possible. One way to help improve performance is to exploit the chemical versatility of organic materials. Many different structures can be synthesised through chemical modification, allowing the optoelectronic properties (such as the optical band gap and energy levels) and physical properties (such as solid state structure) of the material to be tuned. Materials can therefore be chemically designed to optimise their performance in organic electronic devices. This work is focused on exploring the relationship between chemical structure, material properties and device performance, through the design and synthesis of new materials for organic field-effect transistors (OFET) and organic photovoltaics (OPV). The majority of the new materials synthesised in this thesis are new donor-acceptor polymers (Chapters 2-6), in which an electron donating monomer and electron accepting monomer are co-polymerised. Whilst there is a vast wealth of different donor monomer structures available, there has been less focus on the synthesis of new electron accepting monomers. In this work the common electron acceptor monomer 2,1,3-benzothiadiazole (BT) is chemically modified to either increase the solubility (Chapter 2) or increase the electron accepting strength (Chapters 3 and 4). Increasing the strength of the electron accepting unit in donor-acceptor polymers was found to induce N-type (electron conducting) behaviour in OFET devices (Chapter 3) or improve OPV performance by reducing the optical band gap and increasing light absorption (Chapter 4). Power conversion efficiencies of ~6.5% in OPV devices were achieved. In chapter 6 a novel BT based acceptor monomer is designed to maximise polymer backbone planarity which resulted in promising hole mobilities of up to 0.5 cm2/Vs when tested in OFET devices. In Chapter 5 the strength of the common electron accepting unit benzo[d][1,2,3]thiadiazole (BTz) is also increased through chemical modification. Similarly to Chapter 4, we find that increasing the strength of the electron accepting unit of the donor-acceptor polymer improves the OPV performance through increased light absorption, resulting in efficiencies of ~6.5% in OPV devices. Finally in Chapter 7, new electron rich conjugated small molecules are synthesised and the optoelectronic properties investigated.
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Figueiredo, José Maria Longras. "Optoelectronic properties of resonant tunnelling diodes." Doctoral thesis, Universidade do Porto. Reitoria, 2000. http://hdl.handle.net/10216/14347.
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Octon, T. "Optoelectronic properties of two-dimensional molybdenum ditelluride." Thesis, University of Exeter, 2019. http://hdl.handle.net/10871/35713.
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In this thesis the layered, two-dimensional material MoTe2 is examined experimentally for its optoelectronic properties, using a field effect transistor device configuration. MoTe2 experiences a strong light matter interaction, which is highly dependent on the conditions of the measurement, and the wavelength of light used. Light is able to: produce a photocurrent in MoTe2, desorb adsorbates from the surface, and even controllably thin by a single layer at a time. A theoretical study on MoTe2 also provides insights on the source of some of these interesting light matter interactions. MoTe2 is found to be a fast and responsive photodetector when illuminated with red laser light in ambient conditions, with increases in current stemming from the photovoltaic effect. Due to the generated charge carriers from the photovoltaic effect, conductivity can increase by increasing the Fermi energy of the material, or by a photogating effect where excited charges are trapped and behave as an artificial gate for the field effect transistor. The mechanisms of charge trapping are experimentally investigated due to their prevalence in the photodetection mechanisms. A theoretical study points towards the existence of two types of trap states, in not just MoTe2 but all transition metal dichalcogenides, with shallow traps closer to the valence band edge (τ ~ 500 s) and deeper traps (τ ~ 1000 s), further away from the valence band edge. MoTe2, under the effects of higher energy photons from blue and green lasers, showed different photocurrent mechanisms to red light. From the increased energy of the photons, photo-desorption of adsorbates on the surface of MoTe2 occurred causing a decrease in the overall current, in a rarely seen photocurrent mechanism. Again, both shallow and deep traps are evident from the experimental measurements, with the shallow traps being removed when illuminated by higher energy photons. Finally, a humidity assisted photochemical layer-by-layer etching process was developed with an in-situ Raman spectroscopy system, able to thin MoTe2 by a single layer at a time with 200 nm spatial resolution. MoTe2 FETs were created with thinned channels to examine the effect of the thinning technique on optoelectronic properties. Some improvement in optoelectronic performance (higher responsivity, higher mobility) was seen for the thinned channel devices, with great improvement observed for monolayer MoTe2.
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Tong, Wing-yun, and 唐穎潤. "Organic optoelectronic materials: optical properties and 1D nanostructure fabrication." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B38574597.
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Jalili, Yousef Seyed. "Optoelectronic properties of GaAs-based dilute nitrides." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408757.
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Jefferson, Paul Harvey. "Optoelectronic properties of highly mismatched semiconductor materials." Thesis, University of Warwick, 2009. http://wrap.warwick.ac.uk/2228/.
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Dilute nitride alloys of III–V semiconductors, and transparent conducting group-II oxides may both be categorised as highly mismatched compounds. The small size and high values of electronegativity of nitrogen and oxygen (see figure), compared to the substituted anion, in dilute nitrides, and the cation, in transparent conducting oxides, give rise to striking properties in these materials. The dilute nitride alloys GaNSb, InNSb, and GaInNSb, grown by molecular beam epitaxy, have been studied. Infrared absorption measurements of GaNSb are presented, showing the divergence of transitions from the valence band to E− and E+ conduction bands with increasing nitrogen incorporation. The fitting of the positions of the valence band to E+ transitions gives a value of 2.6 eV for the coupling parameter in this material. A reduction in the bandgap of InNSb from that of InSb is shown by modelling the competing effects of Moss-Burstein band filling and bandgap renormalisation. Finally, bandstructure calculations of the quaternary material GaInNSb, with dilute incorporations of nitrogen and indium, show that the material is suitable for the exploitation of the 8–14 μm atmospheric transmission window. Structural characterisation of GaInNSb shows that this material can be grown lattice matched to GaSb with nitrogen and indium incorporations of 1.8 and 8.4 per cent, respectively. The conducting oxide CdO, grown by metal-organic vapour-phase epitaxy, has also been studied. Analysis and simulation of infrared reflectance data, including conduction band non-parabolicity and Moss-Burstein band filling, reveal bandgap and band-edge effective mass values of 2.16 eV and 0.21 m0, respectively. In addition, high energy 4He+ ion irradiation was used to stabilise the Fermi level in CdO. Carrier statistics calculations were performed and the charge neutrality level was found to be 2.52 eV with respect to the "-point valence band maximum, corresponding to 0.36 eV above the conduction band minimum. The location of the charge neutrality level within the conduction band explains the propensity for high unintentional n-type doping, and the high conductivity observed in CdO.
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Flannery, Lorraine Barbara. "Electrical and optoelectronic properties of gallium nitride." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268478.
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Zanato, Daniele. "Optoelectronic properties of Group III-N semiconductors." Thesis, University of Essex, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415640.
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Saadatkia, Pooneh. "Optoelectronic Properties of Wide Band Gap Semiconductors." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1562379152593304.
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Adhikari, Naresh. "Defects and Optoelectronic properties of Zinc oxide." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1562770832047501.
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Laidlaw, W. M. "A study of mixed-valence complexes and their nonlinear optical properties." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297227.
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Wang, Jianpu. "Optoelectronic properties and memory effects of ZnO nanocrystals." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611743.
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Lim, Shuang Fang. "Optoelectronic properties of polyfluorene homo- and co- polymers." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616021.
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James, Grant Robert. "On the growth and characterisation of AIGaN alloys for optoelectronic applications." Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/8824.
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In this study the growth and characterisation of undoped and Si-doped AlxGa1-xN has been performed. The layers were grown using low-pressure metalorganic vapour phase deposition (MOCVD) on sapphire substrates. The optical and electrical properties of the AlxGa1-xN layers were studied using variable temperature Hall effect and photoluminescence measurements. AlxGa1-xN layers were grown over the entire composition range. Room temperature ultraviolet (UV) transmission measurements showed that the material quality was very good for layers with an Al content, x, of 0 _ x _ 0.5. However, the quality of layers of higher composition was seen to rapidly decrease with increasing x. The electrical and optical properties of AlxGa1-xN with x < 0.5 were also good, comparable to those reported on in literature. The study of the Si-doping of AlxGa1-xN was performed in two parts; firstly a series of Al0.23Ga0.77N samples was grown in which the doping level was increased from zero to n _ 3 × 1018 cm-3. A similar, albeit a less rigorous, study was performed for Al0.41Ga0.59N and Al0.5Ga0.5N. A second series of samples was then grown in which the doping level was kept constant, while the Al content was incrementally increased. Room temperature Hall effect measurements performed on Si-doped Al0.23Ga0.77N showed that the electron concentration did not scale linearly with the silane flow, as was the case in GaN. It was also seen that the electron mobility of the layers increased with slight Si-doping, possibly due to an improvement in the crystalline quality and/or a change in the conduction mechanism. It was also found that at higher compositions (x = 0.41 and 0.50) an increase in the doping level resulted in an increase in the mobility. Variable temperature Hall effect and photoluminescence measurements, performed on the Al0.23Ga0.77N samples, revealed a good correlation between the first PL activation energy E1 and the donor activation energy ED, prompting the conclusion that the first PL recombination channel in AlxGa1-xN is due to the delocalisation of excitons bound at neutral Si donors. Furthermore, E1 and ED were seen to decrease with n1/3, as is the case for GaN and other semiconductor materials. It was also observed that strong exciton localisation occurs in slightly Si-doped material, with the amount of localization becoming less at higher doping levels. Possible mechanisms responsible for the second PL recombination channel of activation energy E2 were also proposed. The electrical and optical properties of the second set of AlxGa1-xN samples was then studied. The PL properties of undoped AlxGa1-xN were typical of a homogeneous alloy system, with the increase in the PL FWHM and exciton localisation energies with x following the trend predicted by alloy disorder theory. The variation of the band gap energy with the Al content could not, however, be fitted over the entire composition range using a single bowing parameter. It was proposed that this was due either to an effect of the 9 7 valence band crossover, or due to exciton localisation at alloy disorder and/or impurities. As was the case for GaN and Al0.23Ga0.77N, all undoped material was highly resistive. As was mentioned earlier, the exciton localisation energies increased according to alloy disorder theory in undoped AlxGa1-xN. In the doped samples, however, a large increase in the donor localisation energy was measured for x > 0.3. The possibility that Si could become a DX-centre in AlxGa1-xN was then investigated. However, Hall effect measurements showed that the Si activation energy increased in good agreement with the model of a shallow effective mass state donor, with no sudden increase in ED being observed up to x = 0.4. It was then suggested that the increase in the E1 and E2 activation energies, as well as the exciton localisation energies, could be due to the 9 7 valence band crossover, which occurs at roughly the same composition. However, due to the scarcity of reports on the valence band structure in AlxGa1-xN no conclusions could be made at this stage as to the effect of the 9 7 valence band crossover on the PL properties of AlxGa1-xN.
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Qian, Wenjie. "Preparation and processing of molecular materials with optoelectronic properties." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/664220.
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Materiales orgánicos basados en moléculas pequeñas con propiedades optoelectrónicas son particularmente atractivos en los campos de celdas solares orgánicas y en el campo de la electrónica molecular. Porfirinas y curcuminoides (CCMoids) son moléculas que suscitan interés, siendo buenas candidatas en los campos mencionados, debido a que presentan estructuras químicas modificables y excelentes propiedades electrónicas. En esta tesis, se han estudiado la preparación y diseño de moléculas pertenecientes a las dos familias aquí indicadas, la capacidad de autoensamblaje de dichas moléculas conjuntamente con sus posibles aplicaciones.
En el capítulo II, se han sintetizado dos metaloporfirinas (Zn(4R-PPP) y Zn(PPP)) ligandos largos que contienen centros quirales o aquirales conjutantemente con grupos carbonilos en las cuatro posiciones meso de sus respectivos núcleos de porfirina. Posteriorment, se ha sintetizado un estudio completo relacionado con las interacciones intermoleculares no covalentes de dichas multiporfirinas y experimentos iniciales con la creación de celdas solares orgánicas de hetero-unión (BHJ-OCs) donde este tipo de porfirinas han sido procesadas en solución para el estudio de su comportamiento como sistemas donadores en dichas celdas.
Dicho estudio se extendió en el capítulo III a dos nuevas porfirinas (TEP y Zn (TEP)) con sustituyentes carbonilos pero más cortos donde se investigó el efecto de las dimensiones de los ligandos en las interacciones intermoleculares finales, y cómo esto afecta el rendimiento de OSCs.
En el capítulo IV se explica como con los mismos centros quirales en las posiciones meso, se obtuvo una nueva porfirina, Zn(4R-CPP), que contiene grupos carboxílicos. También se muestran los estudios con dicho sistema y porfirinas adicionales con la formación de sistemas de autoensamblaje binarios basados en interacciones no covalentes o de autoensamblaje iónico para su posible aplicación como nanomateriales.
En el Capítulo V, se sintetizaron CCMoides que contienen grupos quirales, de forma similar al capítulo II, así como el estudio del efecto de la quiralidad de dichos materiales. Además, la investigación hace énfasis en el logro de grupos ácidos terminales a partir de la hidrolización de los grupos ésteres (como se muestra en el capítulo IV) que permitió investigar la posible creación de sistemas con diferente dimensionalidades. Después, en el Capítulo VI, se exploró la síntesis de CPs /redes mediante el uso de CCMoides que contienen grupos piridínicos en sus terminaciones (3Py-CCM).
El último capítulo está dedicado al diseño de nuevos derivados de porfirina que contienen grupos de anclaje basados en azufre para su aplicación en electrónica molecular conjuntamente con el estudio de sus propiedades electrónicas en solución y en estado sólido. Además, una familia de CCMoids también se ha analizado de manera similar a los derivados de porfirina, con el objetivo de recopilar información para mejorar su diseño molecular para aplicaciones electrónicas.Organic small molecules materials with optoelectronic properties are particularly attractive in the fields of organic solar cells and molecular electronics. Porphyrins and curcuminoids (CCMoids) are prospective candidates in these fields due to their modifiable chemical structures and outstanding properties. In this thesis, the design and preparation of these two families of molecules, together with their self-assembly abilities and potential applications have been studied. In chapter II, two metalloporphyrins (Zn(4R-PPP) and Zn(PPP)) containing long chiral or achiral moieties with carbonyl substituents in the four meso-positions of their porphyrin cores have been synthesized. Then, a complete study related to non-covalent multiporphyrin assemblies has been performed, and initial solution-processed bulk heterojunction organic solar cell experiments were presented. To extend the above study, in chapter III, new porphyrins (TEP and Zn(TEP)) with shorter carbonyl substituents have been investigated and the effect of the length of the ligands in intermolecular interactions was studied, searching how this factor affects as well the OSCs performance. With the same chiral centres in the meso-positions, a porphyrin Zn(4R-CPP) involving carboxylic groups was obtained in chapter IV. And the binary self-assembling systems based on its derivations were achieved through non-covalent interaction or ionic self-assembly towards their potential application as active components in nanomaterials. In Chapter V, CCMoids containing chiral groups, in a similar manner as chapter II, were synthesized. In addition, research towards the achievement of terminal acid groups from the hydrolyzation of the ester groups (as chapter IV shows) allowed the investigation of the possible creation of systems with different dimensionalities. Then in Chapter VI, the synthesis of CPs/networks was explored by the use of a CCMoid containing pyridine moieties at its endings (3Py-CCM). The last chapter is devoted to the design of new porphyrin derivatives containing sulphur-based anchoring groups for their application in single molecular electronics together with the study of their electronic properties in solution and solid state. In addition, a family of CCMoids has also been analysed in a similar manner as the porphyrin derivatives, with the aim of gathering information to improve their molecular design for electronic applications.
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Zeisel, Roland. "Optoelectronic properties of defects in diamond and AlGaN alloys." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=962138452.
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Tong, Wing-yun. "Organic optoelectronic materials optical properties and 1D nanostructure fabrication /." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B38574597.
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Al-Ghamdi, Mohammed Saad. "Optoelectronic properties of InP AlGaInP quantum dot laser diodes." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54948/.
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The aim of this thesis is to understand and optimise the optoelectronic properties of InP quantum dot laser diodes which operate in the range around 730nm required for various application such as the photodynamic therapy. The properties of wafers with two barrier widths, 8 and 6nm, each grown at different temperatures, 690, 710, 730 and 750T, and consisting of 5 layers of dots forms from different quantity of deposited material, 2, 2.5 and 3ML, are described and investigated. The laser and multisection devices of these structures are used to determine threshold current density, lasing wavelength, modal absorption, modal gain and spontaneous emission spectra. The modal absorption spectra show three different dot size distributions, small, large and very large dots. Their variation with growth temperature results in a blue shift accompanied by an increasing number of states while the variation with quantity of deposited material shows only an increase to the number of states. The lasing wavelength variation with growth temperature covers a range between 715–745nm. The threshold current density as a function of temperature for 2000/m long laser devices grown at temperature of 750°C exhibits a distinctive dependence on the operating temperature and becomes less pronounced when the growth temperature reduces. This is explained in terms of the carrier distributions in the quantum dot and quantum well states without invoking an effect from Auger recombination. The optimisation of threshold current density can be reached by using structures with higher barrier width grown at low temperature and deposited with high quantity of quantum dot material to minimise both the affect of the very large dot, which contain a number of defects associated with them, and carrier leakage from quantum dot to quantum well states. This reduces the room temperature threshold current density to ISO A/cm 2 for 2mm long lasers with uncoated facets.
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Sims, Marc. "Correlations between structure and optoelectronic properties of conjugated polymers." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269457.
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Sciutto, Andrea. "Synthesis and optoelectronic properties of imidic peri-xanthenoxanthene derivatives." Thesis, Cardiff University, 2018. http://orca.cf.ac.uk/115786/.
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Nowadays polycyclic aromatic hydrocarbons (PAHs) have been the object of study in the search for novel semiconductor materials. Synthetic research in this field is ongoing since the beginning of the century, but it was only in recent years that technological development caused an increased interest for the optoelectronic properties of such systems. As a result, spectroscopic studies revealed interesting properties of peri-xanthenoxanthene (PXX) and its derivatives that will be extensively presented and discussed in this thesis. Concerning the tuning and tailoring of the optoelectronic properties of PAHs, many strategies can be applied in the quest for novel and better performing materials. One of the most common and efficient techniques is the atom doping that consists of a replacement of a carbon atom with a heavier one, such as oxygen or sulphur. In Chapter 1, before addressing the detailed investigation of this thesis work, a brief introduction on the nature and applications of organic semiconductor materials is given. Optoelectronic properties of well-known perylene diimides (PDIs) are compared and the discussion eventually moves to PXX derivatives that are the core of this thesis. In Chapter 2, a variety of synthetic pathways is explored in order to prepare PXX imide derivatives bearing electron-withdrawing groups in the peri position. The bottom-up approach is used to afford novel PXX systems. The synthesis of the desired systems is shown and discussed exploiting the key hydroxynaphthalene anhydride substrate. As a conclusion of this thesis, Chapter 3 deals with the characterisation of the optoelectronic properties of PXX imide derivatives. Furthermore, PXX substrates have been screened as photoredox systems to perform dehalogenation reactions and the mechanism of the photo-triggered chemical transformation has been investigated.
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Manca, Marco. "Study of the optoelectronic properties of atomically thin WSe2." Thesis, Toulouse, INSA, 2019. http://www.theses.fr/2019ISAT0030.
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: Les dichalcogénures de métaux de transition (TMDs) constituent une famille de matériaux lamellaires riches de potentialités en optique et en électronique. La caractérisation des TMDs a permis la découverte de leurs propriétés physiques exceptionnelles : amincis à l’état de mono-feuillets, les TMDs semi-conducteurs deviennent des matériaux à bande interdite directe, donc très efficaces pour l’absorption ou l’émission de lumière. Le gap direct de ces semi-conducteurs est situé aux points K, à la frontière de la zone de Brillouin. Les propriétés optiques sont dominées par les excitons paires électron-trou liées par l’attraction de Coulomb et l’interaction lumière-matière y est extrêmement forte, l’absorption d’un faisceau lumineux pouvant atteindre 20% par monocouche. Outre l’existence du gap, les TMDs se différencient du graphène par leur fort couplage spin-orbite, ainsi que par la rupture de la symétrie d’inversion. En conséquence, les règles de sélection pour les transitions optiques à travers le gap ont un caractère chiral. Les états de spin opposés dans les bandes de valence et de conduction sont significativement clivés en énergie du fait de l’interaction spin-orbite. Cette propriété permet d’exciter optiquement des états de spin et de vallée spécifiques dans l’espace réciproque et de suivre leur comportement dynamique. Ainsi, les TMDs mono-feuillets constituent-ils des systèmes modèles très attractifs pour l’étude de la physique des états de spin et de valléeTransition Metal Dichalcogenides (TMDs) are a family of layered materials with potential applications in optics and electronics. Following the discovery of graphene, TMDs were characterized and extraordinary physical properties were discovered: when thinned down to a monolayer, TMDs become direct band gap materials, therefore strongly facilitating light emission. The direct bandgap of these semiconductors is situated on the edge of the Brillouin zone, at the K-point. This is different from standard semiconductors for optoelectronics like GaAs where the bandgap is in the centre of the Brillouin zone. The optical properties are dominated by excitons, and light-matter interaction is extremely strong with up to 20% of light absorption per monolayer. In addition to a bandgap, TMDs present strong spin-orbit coupling and broken inversion symmetry. As a result, the optical transitions across the bandgap have chiral selection rules. The spin states in the valence and conduction bands are well separated in energy by the spin-orbit interaction. This makes it possible to optically address specific spin and valley states in momentum space and monitor their dynamics. As a result monolayer TMDs are exciting model systems for spin and valley physics: these research fields are termed spintronics and valleytronics. This motivated our work on the exact understanding of the optical transitions, their polarization selections rules and the different exciton states
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Desroches, Maude. "Exploiting the geometry of anthanthrone to harness optoelectronic properties." Doctoral thesis, Université Laval, 2018. http://hdl.handle.net/20.500.11794/29995.
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Depuis quelques années, un intérêt marqué pour les pigments de cuve a fait son apparition dans la littérature. Longtemps considérés comme des produits destinés exclusivement à la chimie fine industrielle, les pigments sont de plus en plus utilisés en recherche académique. Ils sont produits à l’échelle de la tonne pour des sommes avantageuses et leurs structures complexes permettent d’accéder à des molécules prisées en peu d’étapes synthétiques. La plupart de ces pigments sont des hydrocarbures aromatiques polycycliques possédant parfois des hétéroatomes, ce qui en fait des molécules de choix pour l’étude de la relation structure-propriété. En conjonction avec le développement des aromatiques polycycliques, l’étude des composés diradicaloïdes ayant des propriétés hors du commun est en plein essor dans la littérature scientifique. Les travaux présentés dans cette thèse rapprochent donc ces deux domaines. Le cœur anthanthrone, un aromatique polycyclique à la réactivité singulière causée par sa géométrie, permet l’exploration de concepts originaux pour la chimie des composés organiques en couche ouverte. Tout d’abord, un composé à base d’anthanthrone a permis le développement d’une nouvelle méthode pour obtenir des molécules diradicalaires. Il est démontré que la congestion stérique des diphénylméthanes et du cœur anthanthrone se faisant face, facilite une transformation structurelle vers une molécule ayant deux électrons non-appariés. Étonnamment, cette transformation peut avoir lieu à l’état solide en appliquant de faibles pressions. Ainsi, il est possible de briser des liens doubles avec ses propres mains à l’aide d’un pilon et mortier. Ensuite, une molécule similaire utilisant les diphénylamines permet aussi l’obtention de composés en couche ouverte lorsque doublement oxydés. Le produit obtenu est donc isoélectronique à son homologue tout carbone. Encore une fois, la géométrie du cœur anthanthrone produit deux systèmes π perpendiculaires, empêchant la recombinaison des radicaux. Pour poursuivre sur ces composés et augmenter la densité de spin, un polymère « polyradical cation » avec des propriétés optoélectroniques intéressantes a été synthétisé. Finalement, le dernier chapitre de cette thèse exploite toujours la géométrie de l’anthanthrone mais dans un contexte complètement différent. Grâce à la structure unique de l’anthanthrone, il est possible d’obtenir une émission induite par agrégation dans la région du proche infrarougeFor several years, a keen interest in vat dyes emerged in the literature. Long considered exclusively for the specialty chemical industry, pigments are increasingly used in academia. They are mass-produced at a low cost and their complex structures allow valued molecules to be obtained in few synthetic steps. Most of these pigments are aromatic polycyclic hydrocarbons (PAHs) sometimes including heteroatoms, making them molecules of choice for the study of structure-property relationship. With the development of PAHs, the study of biradicaloids having outstanding properties is thriving in the scientific literature. The work presented in this thesis brings together these two fields of study. The anthanthrone core, a polycyclic aromatic with a singular reactivity caused by its geometry, allows for the exploration of original concepts for the chemistry of organic open-shell compounds. First of all, anthanthrone-based molecules allowed the development of a new method to obtain open-shell diradicals. It was found that the steric congestion of the diphenylmethane and the anthanthrone core facing each other, facilitate the structural transformation towards a molecule having two unpaired electrons. Surprisingly, this transformation can proceed in the solid state at low pressures. Thus, it is possible to break double bonds with bare hands using a mortar and pestle. Next, similar molecules with diphenylamines also allow the formation of open-shell compounds when doubly oxidized. The obtained products are isoelectronic to their all-carbon counterpart. Again, the geometry of the anthanthrone core produces two perpendicular π-systems, preventing the recombination of the radicals. To follow-up with similar compounds and increase the spin density, a polymer “polyradical cation” possessing intriguing optoelectronic properties was synthesized. Finally, the last chapter of this thesis still exploit the geometry of the anthanthrone dye but in a completely different context. With the unique structure of this core, it is possible to obtain aggregation-induced emission in the near infrared region.
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Moss, Kathryn Clare. "Novel intramolecular charge transfer materials and their optoelectronic properties." Thesis, Durham University, 2012. http://etheses.dur.ac.uk/3375/.
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A summary of aspects of the literature surrounding organic donor-acceptor systems for a variety of optoelectronic applications (OLEDs, OFETs, OPVs) is presented with a particular focus on two key moieties; 9,9-dialkylfluorene (F) and dibenzothiophene-S,S-dioxide (S). The development of these “building blocks” into novel systems capable of intramolecular charge transfer, i.e. donor-acceptor containing materials, is then discussed. The syntheses and photophysics of a number of novel fluorescent ambipolar trimers based on F and/or S are presented which allow investigations to be performed into the excited state behaviour of the systems. Tuning of the emission colour is demonstrated from deep blue to green by varying the strength of the donor and/or by manipulating the extent of conjugation through the systems. Related trimers are investigated which exhibit the unusual phenomenon of (low temperature) phosphorescence from all-organic systems. Development of the F/S trimers into polymers gives systems which are capable of emitting white light and all-fluorescent white-emitting devices are presented. Following on from this, the use of F as a molecular bridge between donor (ferrocene) and acceptor (C60) moieties is presented, with the aim of modulating charge transfer between the two by varying the linker between ferrocene and F as well as the length of the fluorene bridge. The synthesis and electrochemical behaviour of the compounds is discussed and photophysical studies are currently being undertaken. Finally, random co-polymers of F, S and related analogues are presented to investigate the morphology of such systems with regard to beta phase formation. A number of F and/or S based systems are also presented with the aim of finding novel high triplet energy host materials for OLEDs. The syntheses and photophysical studies of these materials are discussed. Overall, the work demonstrates the great potential of F and S in donor-acceptor systems for a wide variety of optoelectronic applications.
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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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Chuang, Chun-Sheng, and 莊竣盛. "Characterization of ITO glass for its optoelectric and hydrophobic properties." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/3jxd47.
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碩士中原大學
化學研究所
99
In this study, indium tin oxide (ITO) thin film were deposited on the glass by DC magnetron sputtering. We studied the thin-film properties of ITO that have a thin-film thickness of 15nm~175nm, transmittance, resistivity, the intervention effect and the heating effect of current. This study also examines the annealing to decrease resistivity and uses the Sessile Drop to determine hydrophobic and hydrophilic properties on the surface of ITO glass. Indium tin oxide is a transparent conducting thin film that has a highly visible transmission and low resistivity. ITO substrates were usually the conductive electrode of the display. In the touch panel applications, the transparent conductivity oxide (TCO) film requires high resistivity the TCO film should be thin; however, this has many disadvantages, including non-uniform resistivity. Experiments results demonstrate that the ITO thickness of 15nm has 91% transmittance and resistivity 2.81×10-4(Ω-cm). The uniform resistivity of the ITO substrates edge is also good under annealing temperature 290oC process condition.
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Chu-YunHsiao and 蕭竹芸. "Synthesis and Optoelectric Properties of Si Nanocrystal Embedded Si-Rich Oxide Films." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/30463621268795816985.
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博士國立成功大學
電機工程學系碩博士班
101
Si-rich oxide (SRO) with embedded Si nanostructures has attracted considerable attention owing to pronounced quantum effect after annealing, regardless of the indirect band-gap nature of Si. The quantum-confinement properties of Si nanocrystals (NCs) have great potential for applications in light emission devices, photodetectors, and solar cells. Many methods have been reported to prepare the Si NCs embedded in SRO films, including sputtering, evaporation, and plasma-enhanced chemical vapor deposition. Among them, sputtering has several advantages superior to other methods such as low substrate temperature, low cost and good adhesion with substrates. Ion beam is another technique that has been developed to assist depositing optical thin films, particularly used together with evaporation to improve film quality. In this thesis, we prepared SRO films and SRO/SiO2 superlattices by sputtering and ion-beam-assisted sputtering (IBAS), and discus the material characteristic and optoelectric properties. 1. Self-assembled Si/SiO2 superlattice This work involves as-prepared SiOx (x≦2) films that were deposited by reactive sputtering. The regular Si/SiO2 superlattices were self-assembled without post-annealing. The periodicity of Si/SiO2 superlattices was modulated by varying the oxygen flow rate, and was associated with x in SiOx in the range 2-1.3. Si/SiO2 superlattices were formed under compressive stress. The continuity equation of transport and the additional term in the Helmholtz free energy were used to explain the periodicity and the lower limit of the superlattices, respectively. 2. Si-rich oxide films This study exploits the material and optical properties of Si NCs-embedded SRO films prepared by low-energy IBAS. Transmission electron microscopy and X-ray diffraction revealed that the IBAS improved crystallinity of the annealed SRO films. The size and density of Si NCs can be fine-tuned by ion-beam energy and oxygen partial pressure. The phase separation of IBAS-prepared SRO films was enhanced after annealing. This fact was particularly pronounced at low-oxygen partial pressure condition. Visible photoluminescence of the IBAS films was obtained, owing to the quantum confinement effect of Si NCs. 3. Si-rich oxide/SiO2 superlattices This study presents the structure and luminescence properties of SRO/SiO2 superlattices in which the SRO layers were prepared by low-energy (〈60 eV) argon ion-beam-assisted sputtering. Experimental evidence indicates that the density of the Si NCs in the SRO layer was increased by ion-beam treatment after annealing, increasing the surface roughness. Moreover, the stoichiometry of the as-prepared SRO layer was unchanged but the phase separation of the annealed SRO layer was enhanced by the ion-beam treatment, yielding visible white photoluminescence from the E’ centers and Si nanocrystals. 4. Si-rich oxide/SiO2 superlattice LEDs The SRO/SiO2 superlattices LEDs were prepared by varying the structure, substrate temperature, and ion source treatment was reported. The electroluminescences of SRO/SiO2 multilayers were associated with the injection barrier height and Si dots size. The retention time of SRO/SiO2 superlattice deposited by IBAS was longer than that prepared by sputtering. Impedance spectroscopy analyses were to realize the electrical properties of materials and their interfaces.
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Tsai, Yi-Lin, and 蔡易霖. "Fabrication and Optoelectric Properties of 3D-Ordered Porous Films with Core/Shell Nanostructure." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/68038375247861905936.
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碩士國立中正大學
化學工程研究所
99
Our research focuses mainly on the preparation of hematite (α-Fe2O3) thin films with high conversion efficiency. Much of the earlier work on hematite photoelectron chemical (PEC) systems were carried out in the 1970–1980s. Charge collection efficiencies from hematite in PEC cells were very low. However, a few recent studies reported that the poor solar charge collection efficiency was attributed to low minority (hole) diffusion length of α-Fe2O3. If we can design a device to overcome this problem, maybe we can increase efficiency markedly. In this regard, we want to fabricate a honeycomb structure of hematite, because this porous structure can, in principle, reduce the distance of photo generated holes to reach the electrode-solution interface. The high surface area can also increase the solar absorption. We first prepared the template by using self-assembly of polystyrene (PS) nanoparticles. The size of PS can be controlled by monomer and nucleation density. In other words, we can control the template void spaces. Hematite precursor solutions penetrate the void spaces by capillary forces. The inverse opal structure can be obtained, follow by the calcination to remove the template. Unfortunately, the photocurrent density is low, in the 3~5μA/cm2 region. In the next experiment, we combined the core-shell (ITO/α-Fe2O3) with the honeycomb, the charges (e-) are expected to be collected in the ITO core and readily transported to the counter electrode, that will decrease the electron- hole recombination. This idea provides a new opportunity, but the result is not satisfactory (photocurrent density 15~20μA/cm2),perhaps due to the incomplete coverage ofα-Fe2O3 in the core/shell structure. The uncovered ITO will interfere the result. In the future we will investigate to the defeat and refine the structure.
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Pan, Ko-Ying, and 潘科穎. "Studies on Low-dimensional Metal Oxide Nanostructures and Their Surface Modification on Optoelectric and Photocatalystic Properties." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/75719458867038046866.
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博士國立清華大學
材料科學工程學系
102
There are two major parts in this thesis, including Part I: the fabrications, materials characteristics and optoelectronic applications of nanostructures of core-shell SnO2-ZnO, tin-doped indium oxide, and Part II: the syntheses, materials features and optoelectronic applications of nanoparticles of core-shelled silica-silver and silver-embedded aluminum/silica. In the Part I, as for core-shell SnO2-ZnO nanowires, in advance, tin dioxide nanowires were synthesized by thermal evaporation. Then, depositions of ZnO nanolayer on SnO2 nanowires have been successfully synthesized by atomic layer deposition (ALD). These results demonstrated that the SnO2-ZnO core-shell nanowires have potential application as UV photodetectors with high photon-sensing properties. In terms of nanostructures of tin-doped indium oxide, indium oxide (In2O3) nanorods, nanotowers and tin-doped (Sn:In=1:100) indium oxide (ITO) nanorods have been successfully fabricated by thermal evaporation, respectively. Judging from cathodeluminescence (CL) spectra of these three nanoproducts, it is clear that tin-doped (Sn:In=1:100) indium oxide (ITO) nanorods cause a blue shift. No doubt that ITO nanorods obtains the most effective performance among these three nanoproducts, and this also means doping elements in original nanomaterials would be the best way to enhance physical properties. Additionally, this study would be beneficial to the applications of In2O3 nanorods, nanotowers and ITO nanorods in optoelectronic nanodevices, especially in organic light-emitting diode (OLED). In the Part II, as for core-shelled silica-silver nanoparticles, abundant core-shelled silica-silver nanospheres with uniform diameter and morphology were successfully synthesized by Stöber and seed-mediated method, in sequence. Moreover, by the different additions of glucose as the reducing agent, the silver nanoparticles were deposited on silica spheres by redox reaction, and the dimensions of samples were well controlled. The surface plasmon resonance absorption band shifted toward infra-red region and became broader gradually during the dimensions of silver nanoparticles were increased in the growth range. Meanwhile, this intriguing result shows that two absorption characteristics peaks are observed in the spectra while the morphologies of nanoparticles are becoming oval-shaped. The amazing data imply that using core-shelled silica-silver nanospheres efficiently enhances the degradation of the organic pollutants under solar energy, which means the core-shelled silica-silver nanospheres is not only a cost-effective route but an energy-saving way to our planet. In terms of silver-embedded aluminum/silica nanoparticles, in order to improve the time-consumption issue of the above method, substantial silver-embedded aluminum/silica nanospheres with uniform diameter and morphology were successfully synthesized by a modified sol-gel technique, a one-spot method. The chemical durable examinations and antibacterial tests of each sample were also carried out for the confirmation of usages in practical. As a result of above analyses, the silver-embedded aluminum/silica nanospheres are eligible for fabricating antibacterial utensils.
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CHANG, PAO-HSIN, and 張寶鑫. "Study of Optoelectric Properties and Thermal Stability of p-GaN/AgSb and p-GaN/AgMn Reflective Ohmic Contacts." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/73909929432209798269.
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碩士國立清華大學
材料科學工程學系
104
In this study, all the samples AgSb(6 at%), AgSb(2 at%), Ag(150 nm)/Sb(4 nm), AgMn(6 at%), AgMn(4 at%), and Ag(150 nm)/Mn(2 nm) were deposited on the p-GaN by dual E-gun evaporation system. The samples were annealed at 500℃ by three different annealing conditions, furnace annealing(FA) in air ambient for 10 min, rapid thermal annealing(RTA) in O2 ambient for 1 min, and rapid thermal annealing(RTA) in air ambient for 1 min. Thermal stability test were performed by annealing at 400℃in air ambient for 60 min. Optoelectricproperties and thermal stability of p-GaN/AgSb and p-GaN/AgMn reflective ohmic contacts were investigated by SEM analysis, reflectance at 460 nm, sheet resistance of metal film , and specific contact resistance. The result show annealed Ag(150 nm)/Sb(4 nm) could suppress the agglomeration of Ag film. Auger depth profile showed Sb dissolved in Ag film for annealed Ag(150 nm)/Sb(4 nm). The specific contact resistance was 2.7 × 10-3 Ω-cm2 , reflectance was 94% at 460 nm, and sheet resistance of metal film was 0.1 Ω/□ for annealed Ag(150 nm)/Sb(4 nm) contact at 500℃ in air ambient for 10 min. The p-GaN/Sb(4 nm)/Ag(150 nm) reflective ohmic contacts showed good thermal stability.
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Lin, Wei Hao, and 林威浩. "Study of Optoelectric Properties and Thermal Stability of p-GaN/AgSn and p-GaN/AgCu Reflective Ohmic Contacts." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/94939597909791543646.
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碩士國立清華大學
材料科學工程學系
104
This thesis study about optoelectric properties and thermal stability of p-GaN reflective ohmic contacts Sn (2nm) / Ag (150nm), AgSn (2 at%), AgCu (4 at%) and AgCu (8 at%) four specimens which are prepared by due electron guns evaporation and AgCu (T.E.) prepared by thermal evaporation plus a AgCu(S.E.) prepared by single electron gun evaporation six specimens in total. We discuss the effect, including light reflectivity, sheet resistance of the metal thin film, specific contact resistance and thermal stability, on the optoelectric properties of AgSn and AgCu alloy reflective ohmic contacts, be influence by different alloy composition, different annealing methods, including furnace annealing and rapid thermal annealing, and different deposition process. We found that Sn (2nm) / Ag film can inhibit the aggregation of Ag film at high temperature annealing, and there are no aggregation be found on AgSn and AgCu thin film after furnace annealing and rapid thermal annealing, and after aging at 400 ℃ for one hour, the influence on reflectivity, sheet resistance of the metal thin film and specific contact resistance are very small. Comprehensive consideration above-mentioned properties, AgSn (2 at%) and AgCu (4 at%) alloys thin films are excellent. After anneal 5min in air at 500 ℃, the AgSn(2 at%) reflectors produce low specific contact resistance(1.2 × 10-3 Ω-cm2),and even lower after aging(7 × 10-4 Ω-cm2), high reflectivity(102% at 460nm),good sheet resistance of the metal thin film(0.15 Ω/□), and good thermal stability. After anneal 5min in air at 500 ℃, the AgCu(4 at%) reflectors produce low specific contact resistance(8.2 × 10-4 Ω-cm2),and even lower after aging(5.5 × 10-4 Ω-cm2), high reflectivity(102% at 460nm),good sheet resistance of the metal thin film(0.12 Ω/□), and good thermal stability.
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Shih, Sheng-Lih, and 時聖立. "Study of Optoelectric Properties and Thermal Stability of p-GaN/AgPd and p-GaN/AgIn Reflective Ohmic Contacts." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/66776308142827429072.
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Cheng, Yu-Chen, and 鄭宇真. "The researches on the thin film electrical transport properties and the optoelectric characteristics of the OLEDs with different buffer materials." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/33135866089717213121.
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碩士國立成功大學
電機工程學系碩博士班
95
Since the buffer layer and the hole-injection layer can improve the interface roughness problem between the organic materials and the ITO electrode. They also increase the hole-injection efficiency for mole hole-electron to recombine and emit photons in the organic emission layer, and achieve the goals for making OLEDs devices with low driving voltage. In this study, we use the Ni(tmdbta) and ZnF thin film as the hole-injection layer and buffer layer in the OLEDs devices by of thermal evaporation method. In the first phase of this search, we deposited Ni(tmdbta) or ZnF2 thin film with different thickness as hole injection layer and buffer layer to investigate the characteristics of the OLEDs. We also studied the hole injection and impedance analysis and optical- electrical characteristics of the sample with sandwich structure (ITO/ Ni(tmdbta) or ZnF2/cathode). In this study, we found Ni(TMDBAA)’s HOMO between ITO’s EF and NPB’s HOMO, hole-injecting efficiency can be improved; As we chose metal oxide and their work functions are bigger than HOMO of NPB, they could be used for lowering the driving voltage.
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Lo, Yuan Heng, and 羅元亨. "Study of Optoelectric Properties and Thermal Stability of p-GaN/AgPt, p-GaN/AgRu, and p-GaN/AgRh Reflective Ohmic Contact." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/28525157028628000097.
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碩士國立清華大學
材料科學工程學系
104
In this study, all the samples AgPt(6 at%), AgPt(4 at%), AgPt(2 at%), Pt(2 nm)/Ag(150 nm), AgRh(2 at%) and AgRu(2 at%) were deposited on the p-GaN by dual E-gun evaporation system. The samples were annealed at 500℃ by two different annealing conditions, furnace annealing(FA) in air ambient for 10 min, and rapid thermal annealing(RTA) in air ambient for 1 min. Thermal stability test were performed by annealing at 400℃in air ambient for 60 min. Optoelectricproperties and thermal stability of p-GaN/AgPt, p-GaN/AgRu and p-GaN/AgRh reflective ohmic contacts were investigated by SEM analysis, reflectance at 460 nm, sheet resistance of metal film , and specific contact resistance.The result show annealed AgPt(6 at%), AgPt(4 at%),AgRh(2 at%) and AgRu(2 at%) could suppress the agglomeration of Ag film.In AgPt(6 at%) and AgPt(4 at%),Ag would produce lateral diffusion causing electrode leakage phenomenon when aging at 400 ℃ for one hour. Comprehensive consideration above-mentioned properties,AgRu (2 at%) alloys thin films are excellent.After anneal 1min in air at 500 ℃, the AgRu(2 at%) reflectors produce low specific contact resistance(7.4 × 10-4 Ω-cm2), high reflectivity(93% at 460nm),good sheet resistance of the metal thin film(0.2 Ω/□), and good thermal stability. Otherwise, we could also find that the work function of the magnitude of the noble metal element itself could't be the main cause of the magnitude of the specific contact resistance ,when small amount of Ag and a noble metal (Pt, Ru, Rh) alloy is formed.
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Chen, Chien, and 陳謙. "Study of Optoelectric Properties and Thermal Stability of p-GaN/AgTi, p-GaN/AgCo, and p-GaN/AgNi Optical Reflective Ohmic Contact." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/23023888333113170650.
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碩士國立清華大學
材料科學工程學系
104
This thesis study about optoelectric properties and thermal stability of p-GaN reflective ohmic contacts Ti (2nm) / Ag (150nm), AgTi (2 at%), AgTi (4 at%), Co(2nm) / Ag (150nm), AgCo (2 at%), AgCo(5 at%) and AgNi(2 at%) seven specimens which are prepared by due electron guns evaporation.We discuss the effect, including light reflectivity, sheet resistance of the metal thin film, specific contact resistance and thermal stability, on the optoelectric properties of AgTi, AgCo and AgNi alloy reflective ohmic contacts, be influenced by different alloy composition, different annealing methods, including furnace annealing and rapid thermal annealing.The result show annealed AgCo(2 at%) and AgNi(2 at%) could suppress the agglomeration of Ag film. The specific contact resistance was 3.4 × 10-4 and 1.1 × 10-4 Ω-cm2 , reflectance was 94% and 92% at 460 nm, and sheet resistance of metal film was both 0.5 Ω/□ for annealed AgCo(2 at%) and AgNi(2 at%) at 500℃ in air ambient for 10 min. Both AgCo(2 at%) and AgNi(2 at%) reflective ohmic contacts showed good thermal stability.
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You, Zong-Xian, and 游宗憲. "The researches on the electrical transport properties of metal-pc thin film and optoelectric characteristics of metal-pc based light-emitting devices." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/38276853729996092793.
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碩士國立成功大學
電機工程學系碩博士班
92
Since CuPc films play the role of the buffer-layer and the hole-injection layer, improve the problem of OLEDs that the stability of emitting films are insufficient and improve the hole-injecting efficiency for more electron-hole to recombine and enhance the performance of OLEDs. In this study, we fabricate OLEDs with Metal-Pcs as an hole-injection layer to investigate their performance. In the first phase of this research, we make the sample with sandwich structure, ITO/Metal-Pc/cathode. We measure the carrier injecting, transport mechanism, mobility, trap concentration, and hole concentration. Then, we find the preferred thickness of Metal-Pc, to fabricate this structure’s OLEDs, ITO/Metal-Pc(10nm)/NPB(60nm)/Alq3(75nm)/LiF/Al. In this study, we find that as the Metal-Pcs’ HOMO are closed to ITO’s EF(5.0eV) , hole-injecting efficiency can be improved. The smaller mobility, trap concentration, and hole concentration of Metal-Pc can enhance devices’ luminous efficiency.
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CHIANG, PIN-HSUAN, and 江品璇. "Preparation and Optoelectric Properties of Few-Layer Reduced Graphene Oxide Conjugated with Self Welding Silver Nanowire Junctions as Flexible Transparent Conducting Hybrid Films." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/m676a4.
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碩士國立高雄應用科技大學
化學工程與材料工程系博碩士班
106
In this study, flexible transparent conducting hybrid films (TCFs) based on few layer reduced graphene oxide (FrGO) conjugated with hydrolyzed-polyethylene terephthalate (H-PET)-based self-welding (SW) commercial silver nanowires (AgNWs) were fabricated by water-bath assisted dipping coating method. H-PET-based SW-AgNW networks were controlled by the mirror silver reaction with different reaction rates and followed by dip-coated on the H-PET film. Few layer graphene oxide (FGO) were prepared by modified Hummers and low speed centrifuge method. FrGO/SW-AgNW TCFs were further prepared by reduced under sodium borohydride and followed by dip-coated on the H-PET-based SW- AgNWs. Effects of mirror silver reaction rate and FrGO layer on the conducting networks, surface morphology, sheet resistance and transmittance of FrGO/SW-AgNW TCFs are systematically studied. The interaction between AgNWs and FrGO was also further discussed. Results showed that SW-AgNW TCFs can be successfully prepared by water-bath assisted dip-coated and mirror silver reaction. As for optical and electrical characteristics analysis, the gain value of transmittance (GPS) can reach 1.88% (the transmittance is slightly increased from 76.06% to 77.49% ) which induced by the self-welding effect. However, GPS value is decreased with increasing the mirror silver reaction temperature and time. The Gain values of sheet resistance (GES) exhibit mostly negative in nature, the maximum value of GES can remark reduce to 61.06%, confirm the truth of mirror silver reaction with the excellent self-welding effect, as well GES value is also decreased with decreasing the mirror silver reaction temperature and time. Furthermore, the results revealed that FrGO/SW-AgNW TCFs can be successfully prepared by water-bath assisted dip-coated. As for optical and electrical analysis, the gain value of transmittance (GPF) can reach 1.92% (the transmittance is slightly increased from 70.80% to 72.16%). The gain value of sheet resistance (GEF) can remark reduce to 59.9% (the sheet resistance dramatically dropped from 123.6 Ω/sq to 49.5 Ω/sq). For Raman and XPS analysis, the charge transfer behavior between FrGO and SW-AgNWs is observed, which attributed to the bridging effect between FrGO and SW-AgNWs, leading to the increase the number of conductive paths in the networks.
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Chen, Tzung-Te. "Optoelectronic Properties of Semiconductor Nanostructures." 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-0707200812263000.
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Chih-HsuehLan and 藍志學. "Optoelectronic Properties of III-NitrideSemiconductor." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/80333670452470328806.
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Chen, Tzung-Te, and 陳宗德. "Optoelectronic Properties of Semiconductor Nanostructures." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/85121254711223240081.
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博士國立臺灣大學
物理研究所
96
In this thesis, we have reported the optoelectronic properties of the semiconductor nanostructures. In part I, the optical anisotropy in type-I and type-II semiconductor nanostructures have been well investigated through the photoluminescence (PL) and scanning electron microscopy (SEM) measurements. In part II, we have investigated the photoelastic effect and the strain relaxation in semiconductor nanostructures through the electroluminescence (EL), PL, and Raman scattering measurements, which will shift the frequencies of the phonon modes and the band-edge transition energies. The studied samples in this thesis including InAs/GaAs quantum dots (QDs) superlattices, InAs/GaAs0.7Sb0.3 QDs, ZnO nanowires, and Si/Si0.5Ge0.5 multiple quantum wells (MQWs). Part I. Optical Anisotropy in Type-I and Type-II QDs 1. Wire-like characteristics in stacked InAs/GaAs quantum dots superlattices for optoelectronic devices The wire-like characteristics of stacked InAs/GaAs QDs superlattices induced by vertically electronic coupling effect were demonstrated by surface photovoltaic and PL measurements. It was found that the surface photovoltaic signal can be enhanced by up to more than one hundred times due to the wire-like behavior along the growth direction. We also found that the emission from the cleaved edge surface is strongly anisotropic, which suggests a possibility to fine tune the polarization by changing the spacer thickness. Additionally, the EL of stacked QDs near 1.3 μm based on the wire-like characteristics has a much better performance than that of uncoupled QDs. 2. Unusual optical properties of type-II InAs/GaAs[0.7]Sb[0.3] quantum dots revealed by photoluminescence The optical properties of type-II InAs/GaAs[0.7]Sb[0.3] QDs were investigated by PL. It is found that the peak position of PL spectra exhibits a significant blueshift under a moderate excitation level. The observed blueshift can be well explained by the band-bending effect due to the spatially separated photoexcited carriers in a type-II band alignment. We also found that the PL spectra exhibit a strong in-plane polarization with a polarization degree up to 24 %. The observed optical anisotropy is attributed to the inherent property of the orientation of chemical bonds at InAs/GaAs[0.7]Sb[0.3] heterointerfaces. Part II. Strain Effect in Semiconductor Nanostructures 3. Photoelastic effect in ZnO nanorods A novel phenomenon called photoelastic effect has been observed in ZnO nanorods, which causes several intriguing behaviors. With increasing excitation power, it is found that the A1(LO) phonon shows a redshift in frequency, and a blueshift of PL peak energy has also been observed. In addition, the temperature dependent PL spectra behave quite differently under high and low excitation power. All our results can be interpreted well in terms of the photoelastic effect, in which the built-in surface electric field is screened by photoexcited electrons and holes. Through the conversed piezoelectric effect, the internal strain is therefore changed. Our results open a new opportunity to manipulate the physical properties of ZnO nanorods, which should be very useful in the application of optoelectric devices. 4. Electroluminescence enhancement of SiGe/Si multiple quantum wells through nanowall structures The enhancement of light extraction from Si[0.5]Ge[0.5]/Si MQWs with nanowall structures fabricated by electron cyclotron resonance (ECR) plasma etching is presented. It is shown that the ECR plasma treatment does not damage crystalline quality. At a driving current of 5.5×106 A/m2, the light output intensity of the MQWs with nanowall structures shows an enhancement of about 50% compared with that of the original MQWs. In addition to the enhanced light extraction, the improved optoelectronic properties are also attributed to the strain relaxation in nanowall structures. Our result shown here offers a promising potential for creating high power light-emitted-diodes.
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Chang, Hsiu-Ju. "Optoelectronic Properties of III-Nitride Semiconductors." 2007. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2606200718315900.
Full text
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Huang, Yuan-Fu, and 黃元甫. "Optoelectronic Properties of Graphene Triple Heterojunction." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/9rstdy.
Full textAbstract:
碩士國立臺灣大學
物理學研究所
106
Heterostructure, the interface between two non-identical materials are widely used efficient strategy to engineer the electronic and optoelectronic devices. Herein, we have designed a triple heterojunction using graphene sandwiched by p- and n-type semiconductors, P3HT and ZnO. Owing to the atomically thin nature of graphene, the electric field generated at the triple interface in thermal equilibrium can penetrate through graphene to interfere the optoelectronic properties of the semiconducting layers. The existence of unique Dirac cone at the junction gives rise several not yet realized properties. The output performance of such heterojunction based phototransistor can be tuned optically, where external photons can be used as a gate to the detection of other photons carrying different energies. In addition to the broad bandwidth of photon detection, we have demonstrated an efficient color sensitivity of the heterostructure. In the viewpoint of robust global demand for novel functional materials and devices, our strategy paves an important step towards the realization of high performance, multifunctional optoelectronic devices.
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Chen, Cheng-Hsin, and 陳政欣. "Optoelectronic Properties of III-Nitride Semiconductors." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/58653479958427350469.
Full textAbstract:
博士國立臺灣大學
物理學研究所
91
Abstract This thesis concerns with the studies on the optical and electrical properties of III-Nitride semiconductors. Photoluminescence (PL), photoluminescence excitation (PLE), time-resolved photoluminescence, Cathodoluminescence (CL), Scanning Electron Microscopy (SEM), photoconductivity (PC), persistent photoconductivity (PPC), and Raman scattering are carried out to study the physical properties of III-Nitride materials, including GaN/AlGaN superlattices, InAlGaN quaternary alloys, and InGaN/GaN multiple quantum wells. Many peculiar phenomena have been observed, which are very useful for the understanding as well as application of III-Nitride materials. These results are presented as follows. (1) Novel optical properties in GaN/Al0.2Ga0.8N superlattices We report several novel optical properties in GaN/AlxGa1-xN quantum wells, including anomalous behaviors of photoluminescence (PL) spectra and first observation of phonon zone folding by Raman scattering. In the first part, we present photoluminescence (PL), time-resolved photoluminescence (TRPL) measurements in GaN/Al0.2Ga0.8N superlattices with different well widths. The anomalous behavior of luminescence spectra as a function of temperature and the lifetime of excitons are measured. Based on the idea of carrier localization by interface roughness, all the measurements can be clearly understood. Our results thus firmly establish that the underlying mechanism of the luminescence in GaN/Al0.2Ga0.8N superlattices arises from the radiative recombination by interface fluctuations. In the second part, we will provide a demonstration of zone-folding effect on optical phonon in GaN/AlxGa1-xN superlattices measured by Raman spectroscopy. Through the photoluminescence measurements, we show that it is the sharp interfaces between the barrier and well layers of the studied samples which enable us to observe the small Raman shift. Our observed frequency shift is in good agreement with the theoretical prediction. (2) Optoelectronic properties in InxAlyGa1-x-yN quaternary alloys We report excitonic optoelectronic properties of InxAlyGa1-x-yN quaternary alloys grown by metalorganic chemical vapor deposition (MOCVD). In the previous report12, we found that the quantum efficiency (QE) of InxAlyGa1-x-yN is enhanced significantly over AlGaN with a comparable Al content12 and the physical origin of this enhanced QE is not clear. Therefore, we performed the PL and Raman measurements to provide the evidence of enhanced luminescent efficiency is attributed to the existence of alloy clusters13 in the first part. In the second part, we perform scanning electron microscopy (SEM) image and energy dispersive X-ray spectrometry (EDS) measurements to provide a more direct evidence for the model described in the first part. In the third part, we report the observation of the persistent photoconductivity (PPC) effect in InxAlyGa1-x-yN quaternary alloys. We point out that the PPC effect is caused by potential fluctuations in InxAlyGa1-x-yN quaternary alloys. In order to obtain the depth of potential fluctuations, the observed PPC effect was investigated with focus on its decay kinetics at different temperature. Together with the studies on photoconductivity (PC), photoluminescence (PL), photoluminescence excitation (PLE) spectra, we show that potential fluctuations in InxAlyGa1-x-yN quaternary alloys arise from the existence of InGaN-like clusters. (3) Peculiar Optical Properties in InxGa1-xN/GaN Multiple Quantum Wells Because GaN-based materials have hexagonal structure, one may expect that the spectral characteristics of the photoluminescence (PL) will depend on the mutual orientation of the symmetry axis (C6), the wave vector (k), and electric field vector (E) of the light. In the fist part, we develop the simple and nondestructive PL method to detect the crystal anisotropy and to establish the crystal orientation effects on optical properties in InxGa1-xN/GaN multiple quantum wells (MQWs). In the second part, we have investigated the polarization anisotropy in the edge emission of InxGa1-xN/GaN multiple quantum wells (MQWs) by photoluminescence (PL) technique. We found that the PL intensity and peak energy strongly depend on the polarization. The origin of the anisotropy can be attributed to the effects of the transitions due to different hole states. Quite interestingly, we observed a rather pronounced interference pattern in the emission spectra. From the interference spectra, we found that the dielectric constant is also anisotropic, which is expected for a material with wurtzite structure. We point out that the superimposed interference pattern on PL spectra provides a simple and convenient way to accurately determine the refractive index. Due to the non-centrosymmetric hexagonal structures of nitride semiconductors, they exhibit large piezoelectric effect. Several groups have pointed out that the quantum confined Stark effect (QCSE) due to piezoelectric (PZ) field plays a very import role for the luminescence in InGaN/GaN quantum wells (QWs). An interesting aspect among the physical phenomena due to the QCSE or the PZ field is the electric field modulation properties of InGaN/GaN QWs. In the final two parts, we present micro-photoluminescence (μ-PL) and micro-Raman measurements with different optical excitation intensities and/or external electric field in InGaN/GaN multiple quantum wells. The InGaN A1(LO) phonon was found to show a redshift in frequency with the increase of optical excitation intensity and/or external electric field. And a blueshift in PL spectra has been observed when the optical excitation density and/or external electric field were increased. The change in the refractive index was determined accurately from the interference pattern shown in the emission spectra. It was found to be strongly related to the blueshift of PL spectra and the redshift of the InGaN A1(LO) phonon. Based on the screening of the built-in PZ field and hence the resulting variation of the residual strain in InGaN QWs, all the measurements can be clearly understood.
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Shepherd, Whitney E. B. "Optoelectronic properties of organic semiconductor materials : from bulk to single molecule." Thesis, 2012. http://hdl.handle.net/1957/35896.
Full textAbstract:
The behavior and application of organic semiconductor materials depend strongly on their molecular structure, and molecular interactions. Several studies of intermolecular interactions in functionalized polyacene materials are presented. The degree and onset of aggregation of a functionalized anthradithiophene derivative was studied as a function of concentration in two different host matrices. The molecular environment was found to influence the degree and onset, but not the nature of aggregate formed. The effect of aggregation on photoconductivity was also studied.
In a blend of two different anthradithiophene derivatives, the intermolecular separation was found to affect the nature of the interaction, transitioning from energy transfer at large intermolecular distances to the formation of an emissive excited state complex at smaller intermolecular distances. This complex was shown
to have effects on both photoluminescence and photoconductivity.
Finally, a single molecule fluorescence microscopy system was built and characterized. Software was written to process data produced from the system and several classes of functionalized polyacenes were studied at the single molecule level. In particular, the photophysics and molecular orientation of various derivatives were quantified. A new solution-processable, photoconductive, polycrystalline host material was found to be suitable for single molecule imaging, and the molecular orientations of individual molecules were found to depend on both their molecular
structures and their local nano-environment.Graduation date: 2013
49
Chiu, Jiann Jong, and 曲建仲. "Organic Semiconductor Nanostructures and Their Optoelectronic Properties." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/84831288157159606745.
Full textAbstract:
博士國立臺灣大學
電機工程學研究所
92
Nanotechnology has become an important and popular research subject recently, because the quantum size effect of nano-structured materials, such as nanowires and nanoparticles, may induce new optical and electronic properties compared with those of conventional materials. Much attention is then turned to nanometer-sized organic materials due to many unique properties such as flexibility, high photoconductivity, and nonlinear optical effects that may offer novel applications in nano-optoelectronic devices. In this study, a widely-used material of organic light emitting diodes, tris-(8-hydroxyquinolate)-aluminum (AlQ3), is employed to fabricate the nanoparticles (zero dimension), nanowires (one dimension), and nanoscaled crystalline films (two dimension). The AlQ3 nanostructures were synthesized by vapor condensation. The average sizes of the spherical nanoparticles are varying from 50 to 500 nm. The surface of the nanoparticles is quite sleek and smooth like that of pearls. The X-ray diffraction (XRD) patterns reveal that the nanoparticles have an amorphous structure. The photoluminescence spectra of the nanoparticles show a broadened peak varying from 4500 Å to 7000 Å, with the maximum intensity at about 5380 Å. The maximum intensity increases as the particle size decreases, owing to the specific surface area. The larger specific surface area of the smaller nanoparticles increases the optical absorption and further enhances the intensity of luminescence. The AlQ3 nanowires were grown on the indium tin oxide (ITO) coated glass substrate. The diameter and length of the nanowires are about 30 to 50 nm and over 1 m, respectively. According to the XRD and high resolution transmission electron microscopy (HRTEM) analysis, the nanowires reveal an amorphous structure. The AlQ3 nanowires exhibit a low turn-on field of 8.0－10.0 V/m and a maximum current density of about 15 mA/cm2. The field enhancement factor is estimated to be 275. A stable emission current can be performed, thus the field emission of organic semiconductor nanowires was first demonstrated. It indicates that the application of this organic semiconductor in field emission is quite promising. The nanoscaled AlQ3 crystalline film was synthesized on the ITO coated glass substrate. It was stacked with nanometer-sized rods, approximately 100 nm wide and 1 μm long, and had a surface roughness of about 100 nm. The vibronic progression with several separated peaks was observed in the photoluminescence spectrum at room temperature. It is attributed to the crystallinity of AlQ3 and the coupling of vibrations of the individual ligands to the fluorescence transition. The emission current was also observed with a turn-on field of 12.0 V/μm, and a current density of about 0.8 mA/cm2 at 22 V/μm. A stable emission current can also be performed. It demonstrates that the electrons emit from the bumps of the AlQ3 crystalline film at high voltages. Therefore, the AlQ3 crystalline film provides a new choice for field emission. According to the Fourier transfer infrared (FTIR) spectrum, the chemical bonding of AlQ3 is preserved in the nanoparticles even after evaporation at 410°C. Moreover, all the AlQ3 nanostructures remain stable in the field emission gun scanning electron microscopy (FEGSEM) or transmission electron microscopy (TEM) for more than 3hr without any change of the surface morphology, indicating an excellent thermal stability. The chemical bonding and surface morphology of the AlQ3 nanostructures are also preserved after aging in air at room temperature for more than one week.
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Li, Chia-Wei, and 李家偉. "Synthesis and Optoelectronic Properties of Hyperbranched Polyfluorenes." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/09218288582519406356.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
95
Fluorene-based conjugated polymers (PFs) have emerged as a very promising class of blue-light emitting materials for use in PLEDs because of their high thermal stability, high electroluminescence quantum efficiencies. However, one drawback has limited the application of polyfluorene in blue PLED. For example, excimer, aggregation and keto defect were observed and the formation of these interaction reduced PL and EL efficiency. In this study, we prepared dendritic structure in side chain and branch unit in main chain to suppress long wavelength emission under annealing in thin films. Polyfluorene was named as PF. Linear with zero and one generation dendritic structures were named as PLG0 and PLG1, respectively. Hyperbranched with zero and one generation dendritic structures were named as PHG0 and PHG1. The thermal decomposition temperature (Td) of PF, PLG0, PLG1, PHG0 and PHG1 are 469, 402, 374, 413 and 377℃, respectively, and showed good thermal stability. Annealing studies under nitrogen were showed PHG1 couled suppressed long wavelength emission apparently. It proves dendritic group in side chain and branch unit in main chain to suppress aggregation or excimer formation. In electrochemical property of these polymers were investigated. One generation dendritic structure polymers could lower the HOMO energy level. In double layer LED device, the turn-on voltages were 4.7 V, 5.1 V, 5.2 V, 4.2 V and 4.4 V, and maximum luminance was 950 cd/m2, 390 cd/m2, 72 cd/m2, 2106 cd/m2 and 23 cd/m2. The EL spectra of all polyfluorene derivatives showed four emission peaks.