Dissertationen: „Optoelectronic properties of nanoparticles“

1

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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2

Sinha, Banita. „Physicochemical and theoretical investigations on the synthesis characterization and optoelectronic properties of nanoparticles“. Thesis, University of North Bengal, 2016. http://ir.nbu.ac.in/handle/123456789/2625.

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3

García, Castelló Núria. „Atomistic study of structural and electronic transport properties of silicon quantum dots for optoelectronic applications“. Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/145640.

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Introduction It is undisputed that the silicon became the material most widely used in electronics in recent decades[1,2]. The qualities of silicon are well known, from its abundance and low cost to its ability to easily combine with oxides, so that the material has become essential in integrated electronic circuits and CMOS technology. A step further, though, is the idea of integrating electronics and photonics on the same silicon-based technology[3]. However, new strategies are needed to overcome the two principal obstacles of a possible bulk Si photonics: the indirect band gap and the band gap amplitude, suitable for operation only in the infrared range. Due to the quantum confinement of electric charges in silicon quantum dots (Si QDs)[4], the value of the energy gap of the material increases as the size of QD decreases, giving values greater than bulk Si and making Si QDs good candidates for tunable-band gap devices. Several applications have been developed in recent years using these new properties, from light-emitting devices [5] to solar cell tandem type [6] or other opto-electronic devices [7]. Objectives of this Thesis This Thesis initiated a collaboration between our group and the group of Prof. Ossicini of the University of Modena and Reggio Emilia, who has been modeling Si QDs for the last five years[8-14]. In this context, we contributed with the capacity to study the transport properties of these models by taking advantage of mixing two different techniques, Transfer Hamiltonian (TH) and Density Functional Theory (DFT). Thus, the aim of this work was to develop an approach to study transport in nanostructures by taking advantage of the atomistic information that ab initio methods can provide. In particular, the transport through a single Si QD embedded in a SiO2 dielectric matrix and the influence of the Si QD size, the amorphization level, and the doping were studied. Results and conclusions About the size of QDs In the case of embedded QDs of few nanometers, the strong non-planar interface between Si and SiO2 require a different treatment with respect to common planar Si/SiO2 devices. In this PhD Thesis, we have shown that, for small QD sizes, the particle-in-a-box model cannot describe accurately DOS and band offset, because of the large contribution of interface states. In this regime an ab initio approach is necessary to take into account the atomistic detail of the interface between the Si QD and the first shell of O atoms surrounding it. Regarding the electronic transport in Si QDs, a correlation between electron (hole) barrier value and electron (hole) current was found, obtaining larger current values for smaller energy barriers. Specifically, a contrary dependence on Si QD size and amorphization level is found for electron and hole current. On one hand, electron (hole) current is higher for large (small) Si QDs, and, on the other hand, it is enhanced for amorphous (crystalline) systems. On the effects of doping Finally, the DFT-TH technique was used to study the influence of impurity atoms, B for p-doping and P for n-doping, in embedded Si QDs. It is remarkable that this study is one of the first attempts to model with DFT the inclusion of impurity atoms in embedded Si QDs, after the wide knowledge of ab initio works on free-standing Si QDs of the last years. The principal features that we found were: • The impurity positions with lower formation energy are inside the dot for P-doping (P-dot) and at the interface for B-doping (B-int). • Relation between shift of the Fermi energy and improvement of conductivity in doped systems (due to the change in energy barriers). • Improvement of the conductivity for the most energetically favorable position of P-doping (P-dot) but not for the position of B-doping (B-int). • Change in the conductivity between doped and undoped is higher for P-doping than B-doping for a given Si QD size and impurity position, and decreases with QD size for a given specie and impurity position. Bibliography [1] M. Segal. Material history: Learning from silicon. Nature, 483, S43 (2012). [2] H. J. Leamy and J. H.Wernick. Semiconductor silicon: the extraordinary made ordinary. MRS Bulletin, 22, 47 (1997). [3] X. Hao, E.-C. Cho, G. Scardera, Y. Shen, E. Bellet-Amalric, D. Bellet, G. Conibeer and M. Green. Phosphorus-doped silicon quantum dots for all-silicon quantum dot tandem solar cells. Sol. Energ. Mat. Sol. C, 93, 1524 (2009). [4] J. P. Proot, C. Delerue and G. Allan. Electronic structure and optical properties of silicon crystallites: Application to porous silicon. Appl. Phys. Lett., 61, 1948 (1992). [5] Y. Berencen, J. M. Ramirez, O. Jambois, C. Dominguez, J. A. Rodriguez and B. Garrido. Correlation between charge transport and electrolumi-nescence properties of Si-rich oxide/nitride/oxide-based light emitting capacitors. J. Appl. Phys., 112, 033114 (2012). [6] G. Conibeer, I. Perez-Wur, X. Hao, D. Di and D. Lin. Si solid-state quantum dot-based materials for tandem solar cells. Nanoscale Res. Lett., 7, 193 (2012). [7] L. Pavesi, L. D. Negro, C. Mazzoleni, G. Franzo and F. Priolo. Optical gain in silicon nanocrystals. Nature, 408, 440 (2000). [8] M. Luppi and S. Ossicini. Ab initio study on oxidized silicon clusters and silicon nanocrystals embedded in SiO2: Beyond the quantum confinement effect. Phys. Rev. B, 71, 035340 (2005). [9] R. Guerra, I. Marri, R. Magri, L. Martin-Samos, O. Pulci, E. Degoli and S. Ossicini. Silicon nanocrystallites in a SiO2 matrix: Role of disorder and size. Phys. Rev. B, 79, 155320 (2009). [10] R. Guerra, E. Degoli and S. Ossicini. Size, oxidation, and strain in small Si/SiO2 nanocrystals. Phys. Rev. B, 80, 155332 (2009). [11] R. Guerra and S. Ossicini. High luminescence in small Si/SiO2 nanocrystals: A theoretical study. Phys. Rev. B, 81, 245307 (2010). [12] R. Guerra, E. Degoli, M. Marsili, O. Pulci and S. Ossicini. Local-fields and disorder effects in free-standing and embedded Si nanocrystallites. Phys. Status Solidi B, 247, 2113 (2010). [13] R. Guerra, M. Marsili, O. Pulci and S. Ossicini. Local-field effects in silicon nanoclusters. Phys. Rev. B, 84, 075342 (2011). [14] M. Govoni, I. Marri and S. Ossicini. Auger recombination in Si and GaAs semiconductors: Ab initio results. Phys. Rev. B, 84, 075215 (2011).
Les nanopartícules de silici (silicon quantum dots, Si QDs, en anglès) són interessants materials que es proposen com a candidats per a la tercera generació de cel•les solars. Degut al confinement quàntic de les càrregues elèctriques dins del QD, el valor de l'energia de gap del material augmenta a mesura que la mida del QD disminueix, donant valors més gran que el Si bulk i fent que els QDs de Si siguin uns bons candidats per a dispositius amb valors de l'energia de gap modificables. En aquesta Tesi Doctoral proposem un marc teòric per estudiar el transport electrònic en nanoestructures aportant una descripció ab initio dels estats electrònics, basant-se en l'ús conjunt de dues tècniques: la Teoria del Funcional de la Densitat (Density Funcional Theory, DFT, en anglès) pel modelatge de la densitat d'estats del dispositiu i el Hamiltonià de Transferència (Transfer Hamiltonian, TH, en anglès) per la descripció del transport electrònic. Les principals conclusions d’aquesta Tesi Doctoral són: • En el cas de QDs de Si de pocs nanometres dins de matrius dielèctriques, la interfície fortament no-planar entre el Si i el SiO2 requereix un tractament diferent de la communtment utilitzada en l'heterojunció planar Si/SiO2. En aquesta Tesi Doctoral hem observat que, per Si QDs de mida petita, el model de partícula-dins-d'una-caixa no descriu les densitats d'estats i les barrers de potencial d'una forma acurada. Això és degut a què aquest model no recull l'efecte de la interfície, propietat que sembla ser essencial en la mida nanomètrica. • Respecte el transport electrònic en QDs de Si, Per una banda, el corrent d'electrons (forats) és més gran per a QDs DE Si de mida més gran (petita), i, per l'altra banda, el corrent d'electrons (forats) és més important per a sistemes amorfs (cristal•lins). • Les principals influències de dopatge tipus p (amb B) i tipus n (amb P) és (1) les configuracions de més baixa energia de formació són dins del QD quan dopem amb P, i a la interfície entre el QD i la primera capa d'oxígens quan dopem amb B, i (2) hi ha un millora en la conductivitat per la posició energètica més favorable pel dopatge amb P però no per la posició pel dopatge amb B.

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Taha, Hatem. „Optoelectronic and mechanical properties of Sol-Gel derived Multi-Layer ITO thin films improved by elemental doping, Carbon Nanotubes and Nanoparticles“. Thesis, Taha, Hatem (2018) Optoelectronic and mechanical properties of Sol-Gel derived Multi-Layer ITO thin films improved by elemental doping, Carbon Nanotubes and Nanoparticles. PhD thesis, Murdoch University, 2018. https://researchrepository.murdoch.edu.au/id/eprint/41359/.

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Transparent conductors (TCs) are an essential ingredient in numerous new applications which are emerging in the 21st century including high efficiency solar cells, rigid and tactile displays, light emitting diodes, photonics for communications and computing, energy efficient and smart windows and gas sensors, since they allow efficient light transmission while electric signals are applied or collected. So far, indium tin oxide (ITO) reflects the best trade-off between low electrical resistivity and high optical transparency, making it the first candidate as transparent conductor for most optoelectronics technologies despite its drawbacks such as expensiveness and poor mechanical characteristics. However, due to the intricacy of ITO, the coating characteristics strongly depend on the deposition conditions. Despite many developments in ITO-based transparent conductive coatings; these coating are yet to be commercialized for optoelectronic applications. Many challenges still exist in terms of the fabrication of high quality ITO-based transparent conductive coatings, in order to meet the criteria of better, cost-effectiveness and environmentally-friendly characteristics, especially in the context of transparent conductive electrodes. In this study, the deposition conditions along with incorporating thin ITO films with transition metals (Ti and Ag), carbon nanotubes (e.g., SWCNTs) and metals nanoparticles (Ag and Au nanoparticles) were optimized to synthesize high quality ITO based TCs via a facile, environmentally friendly and cost-effective sol-gel spin-coating method. ITO thin films were fabricated with different Ti and Ag doping concentration, different annealing temperature and different geometry such as single layer, bi-layer and multi-layer. The structural, surface morphology and composition, electrical, optical and mechanical properties were characterized using a wide range of complementary techniques, namely, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electron dispersive X-ray (EDX), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), four point probes and Hall Effect, UV-Vis, nanoindentation and FEM modeling. All the fabricated ITO-based TCs showed a nano-sized grain-like morphology forming a homogenous surface structure. XRD results demonstrated a relatively good crystallinity of ITO-based thin film coatings after applying a suitable heat treatment. XPS and EDX analysis corroborated the existence of the main elements for each case of thin ITO coating. In the case of pure ITO and (Ti- and Ag-) doped ITO thin films with a thickness of 350 ±5 nm and 500 C annealing temperature, the highest optical transparency was determined to be 92% for pure ITO, 4 at.% Ti-doped ITO and 2 at.% Ag-doped ITO thin films, while the lowest electrical resistivity of 1.6×10-4 Ωcm was achieved for the ITO film prepared with 4 at.% Ti content. However, these thin films exhibit mechanical characteristics namely hardness and Young’s modulus in the range of (5.3 – 6.8) GPa and (128 – 148) GPa, respectively. In order to enhance their mechanical characteristics while maintaining their optoelectronic properties, SWCNTs were incorporated with ITO with different films thicknesses (i.e. 150, 210, 250 and 320) ± 5 nm, and the characterizations were carried out with respect to the film thickness. The hardness and Young’s modulus for SWCNTs/ITO thin films were in the range of (22 – 28) GPa and (254 – 306) GPa, respectively. The lowest electrical resistivity of 4.6×10-4 (Ω cm) was achieved for the thicker film, while the highest transmittance of 91.5 % was obtained from the thinner film. Obtained results show a significant improvement in the mechanical properties of SWCNT/ITO thin films compared with their counterparts of pure and doped ITO thin films, along with distinctively good optoelectronic properties. To minimize the consumption of indium, ITO thin films were combined with (very thin metal-, metal nanoparticles- and metal oxide-) layers in bi-layered and tri-layered geometries of (AuI), ((Au)nI), ((Ag)nI) and ((AgO)I), and (IAuI), (I(Au)nI), (I(Ag)nI) and (I(AgO)I), respectively, with films thicknesses (~ 130 ± 5 nm). For these coating systems, the lowest electrical resistivity 1.2×10-4 Ωcm was for ITO/Au/ITO thin film, while the highest optical transparency ~ 91.5% was for ITO/AgO/ITO thin film. Two thin films with the configurations of ITO\AgO\ITO and AgO\ITO for tri-layer and bi-layer coatings, respectively with the best optoelectronic performance were nominated as transparent conductive electrodes in designing inverted organic solar cells, and compared with pure ITO thin films. Power conversion efficiencies of 4.9%, 4.2% and 3.8% were found for ITO/AgO/ITO, AgO/ITO and ITO thin film coatings, respectively. To conclude, sol-gel spin-coating derived ITO based transparent conductive coatings present high quality crystal structure, distinctively good optoelectronic properties as well as reasonably mechanical characteristics, and comparable with those achieved from other sophisticated fabrication techniques such as sputtering, pulsed laser deposition, electron beam evaporation etc. All these attributes render the ITO-based coatings promising as transparent conductors in many industrial and technological applications.

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Aghili, Yajadda Mir Massoud. „An investigation on the electrical and optical properties of thin films of gold nanoislands“. Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/18963.

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In this thesis the electrical conduction mechanism and some of the optical properties of thin films (TFs) of gold nanoislands (GNIs) are studied to utilize them for applications in nanoelectronics, sensors, solar cells, and plasmonics. In a regular array of GNIs where NIs have an identical size and tunnel gap, the tunnel current can be calculated by using a relatively simple formula (provided in chapter one). In discontinuous GTFs, there are distributions of GNI sizes and tunnel gaps. Therefore, calculating the tunnel current in such systems at low and high applied voltages over a wide temperature range will be challenging. Here, we introduce a conduction percolation model where uncorrelated broad probability distributions for both the tunnel junction gaps and the Coulomb blockade energies are assumed. An excellent agreement is achieved between model calculations and experimental results at low and high applied voltages over a wide temperature range (2-300 K). In discontinuous GTFs where the Coulomb blockade energies become significantly small such that the tunnel resistance is not much higher than the GNI resistance, the metallic behaviour of GNIs and the thermal expansion of the substrate can play an important role in the temperature dependent resistance of discontinuous GTFs. In this thesis, the temperature dependence of the electrical resistance of discontinuous GTFs at temperatures between 2 K and 300 K is studied experimentally and by model calculations. We show that the tunnel junctions and the Coulomb blockade energies are important at low temperatures and that the thermal expansion of the substrate and the resistance of the GNIs affect the resistance at high temperatures. We obtain a simple expression for the temperature at which the resistance changes from non-metal-like behaviour into metal-like behaviour. iv To show an application of the discontinuous GTFs in nanoelectronics, we measure their resistances over a temperature range of 10-300 K. One of the samples essentially shows a temperature independent resistance (~ 2% resistance variation over a temperature range of 10-300 K). We find that such behaviour corresponds to the minimized Coulomb blockade energy (approximately 0.3 meV). This is achieved by reducing the nearest neighbour distance and increasing the size of the GNIs. It is shown that the temperature independent resistor operates in a regime where the thermally activated electron tunnelling is compensated by the metallic behaviour of the GNIs. Generally, z-scan measurements can be used to demonstrate the nonlinear light absorption in gold, but in TFs, scattering of light from the surface due to its roughness can introduce inaccuracy in measuring absorption nonlinearity. We overcome this problem by developing an experimental technique where a GTF is irradiated by a Nd-YAG pulsed laser at the wavelength of 532 nm in near resonance with the d-band transition of gold. The temperature increase in the GTF is estimated for different light intensities by electrical measurement. Then, the temperature increase is calculated by using a 1D heat transport equation by assuming a constant absorbance for the GTF at the low laser intensities. The comparison between results of the calculations revealed the nonlinear absorption in the GTF. We employed this deviation from the linear behaviour to determine the nonlinear absorption coefficient. It is shown that the nonlinear absorption is due to smearing of the Fermi distribution, and scattering of the light from the surface dose not play a major role in the temperature increase of the GTF. To demonstrate an application of discontinuous GTFs in opto-electronics, we use a discontinuous GTF to rectify an oscillating tunnel current at ultra high frequency (optical frequency). This is done by irradiating the GTF with a Nd-YAG pulsed laser at the v wavelength of 532 nm while a high DC voltage is applied to the sample. The tunnel current is found to be strongly enhanced by partial rectification of the plasmon-induced AC tunnel currents flowing between adjacent GNIs. In addition, our technique shows that the enhancement is due to the plasmon oscillation and the thermal effects seem not to contribute to the tunnel current enhancement.

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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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7

Beliatis, Michail. „Laser fabrication of plasmonic metal nanoparticles for optoelectronic devices“. Thesis, University of Surrey, 2011. http://epubs.surrey.ac.uk/761383/.

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Metal nanoparticles (MNP) are widely researched for the fabrication of novel low cost and more energy efficient optoelectronic devices. MNPs, which exhibit surface plasmon resonance (SPR), can be incorporated into thin film photovoltaic structures and as well as into substrates for enhancing the Raman spectroscopy performance. Recent demonstration of devices with plasmonic structures has limited utility due to the need for techniques of ordered MNPs for large area fabrication that are not currently available. This work examines the suitability of laser annealing for the fabrication of metal nanoparticles in large area optoelectronic devices, as well as the potential for tuning their optical properties precisely within the structure. Gold (Au), silver (Ag) and AuAg alloy particles were fabricated with laser annealing and fully characterized. Morphology characterization of the metal nanopartlcle films (MNFs) with scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed the control over the size by adjusting initial film thickness· and laser fluence. Optical characterization with UV-VIS spectrometry demonstrated that SPR of MNFs can be tuned by adjusting the alloy composition, the dielectric constant of surrounding medium, and the size distribution. This experimental result was confirmed by simulations. Direct incorporation of large well distributed Au nanoparticles into solar cells demonstrated enhanced performance. Dense MNFs with small particles decreased the photovoltaic efficiency. By contrast, in the case of Raman, small alloy particles with SPR wavelength close to the pump wavelength demonstrated the best enhancement. High resolution metal nanoparticle tracks written by the laser demonstrated gas sensing with good sensory capability. However, their high resistivity imposes difficulties in measurements. We conclude that with suitable optimisations the laser annealing technique studied here could be utilised for the fabrication of metal nanoparticles in large area optoelectronics devices. We demonstrate a number of such applications including solar cells and gas sensors and study the effects of metal nanoparticles within these devices in this thesis.

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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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9

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“. Tese, Universidade do Porto. Reitoria, 2000. http://hdl.handle.net/10216/14347.

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11

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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14

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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15

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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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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17

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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18

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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19

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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20

Somani, P. R. „Optoelectronic properties of dye sensitized conducting polypyrrole films“. Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2001. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/6159.

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21

MASALA, SILVIA. „Synthesis and characterization of semiconductor nanoparticles and hybrid nanocomposites for optoelectronic applications“. Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/14820.

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Interest in nanoparticles and nanocomposites of hybrid organic/inorganic materials has increased considerably over the last decade, an interest that has been fueled by novel and exciting potential applications of these materials as electronic devices such as organic light emitting diodes, solar cells and sensors. Group IV semiconductors as well as compounds formed with group II-VI elements are among the most used inorganic materials in this field, mainly because their physical properties can be significantly altered at the nanoscale. The focus of this thesis is on the realization and the study of size-dependent modification of the electronic properties of two classes of semiconductors, germanium (Ge) and cadmium sulfide (CdS). An investigation of the physical properties of Ge nanocrystals prepared by a consolidated method, so as to achieve nanostructures on silicon dioxide substrates, is presented. Concerning the synthesis of CdS, a rapid and inexpensive method that avoids the mixing of toxic reagents and solvents has been developed for the preparation of colloidal nanoparticles and (CdS)nanoparticle/polymer nanocomposites. In particular the CdS based nanocomposites were realized by two main classes of synthesis: ex- and in-situ. With respect to the former class, the nanocrystals were synthesized in a solvent, then extracted and subsequently combined with a polymer. In the case of the latter class, the nanocrystals were produced directly in the polymer matrix. In both cases the nanoparticles were synthesized by adopting the method of the thermolysis of a single source precursor. Beyond the synthesis, several characterization techniques have been employed to study the chemico-physical, optical and structural properties of both the Ge and CdS nanoparticles and nanocomposites. These include Scanning Tunnel Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS), Nuclear Magnetic Resonance (NMR), Fourier Transform-Infrared Spectroscopy (FT-IR), UV-Vis absorption and photoluminescence (PL) spectroscopy, Atomic Force Microscopy(AFM), Transmission Electron Microscopy (TEM), Wide Angle X-ray Scattering (WAXS) and Grazing Incidence x-ray Diffraction (GID). This thesis may be divided into four main areas of study: 1)With the aim of investigating quantum size effects in Ge nanoparticles, high density Ge nanoparticle samples have been realized via a method of high temperature vacuum evaporation onto SiO2 substrates. By means of electrochemical photocurrent measurements, (a) the ability of the Ge nanoparticles to generate photocurrents in the near ultraviolet and visible spectral ranges and (b) the strong dependence of the photocurrent features on the Ge nanoparticle size are demonstrated. 2) Concerning the II-VI compounds, CdS nanoparticles have been fabricated by thermolysis of a Cd precursor in octadecene (ODE), an ex-situ method. Sample preparation under varying conditions-precursor concentration, temperature, and annealing time and rate was carried out. Some examples of dispersion of nanoparticles in polymers are also presented. 3)In accordance with an in-situ method,CdS nanoparticle-based nanocomposites have been prepared by thermolysis of a Cd precursor in different polymeric matrices,firstly employing a dielectric polymer (e.g. Topas, Tp) and then later conductive polymers like poly(N-vinylcarbazole) (PVK) and poly(3-hexylthiophene) (P3HT). Success in the synthesis of CdS nanoparticles in the 2-5 nm (diameter) range for all polymers employed is demonstrated. Particle size is enhanced by increasing the annealing temperature. 4)Electrical properties of nanocomposites prepared via both methods have been investigated by realizing simple stack devices, e.g. ITO-CdS/polymer-LiF-Al (ITO = indium tin oxide substrate). Such devices were studied by performing current-voltage, electroluminescence and photocurrent measurements.It is deduced from different experiments that the synthesis method adopted can be extended to several polymer producing nanocomposites with improved electro-optical properties.

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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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25

Tong, Wing-yun, und 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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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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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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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 vallée
Transition 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 infrarouge
For 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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Sutradhar, Tanushree. „Theoretical investigation on optoelectronic properties of nanoclusters and conjugates“. Thesis, University of North Bengal, 2021. http://ir.nbu.ac.in/handle/123456789/4750.

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Stanislavov, A. S., L. B. Sukhodub, V. N. Kuznetsov, Леонід Федорович Суходуб, Леонид Федорович Суходуб und Leonid Fedorovych Sukhodub. „Magnetite-polymer Nanoparticles: Structure and Properties“. Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42573.

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The paper describes synthesis of magnetite-alginate composites. The main feature of such biomaterials is the simultaneous formation of magnetite nanoparticles inside the alginate matrix. Obtained samples were characterized by X-ray diffraction and transmission electron microscopy. In several samples the secondary phase of ammonium chloride was observed. The average crystallite sizes of magnetite phase are about 13 nm. The addition of alginate leads to the decrease of microstrains in [h k 0] direction.

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Oleynik, Nikolay. „MOVPE growth and characterisation of ZnO properties for optoelectronic applications“. [S.l.] : [s.n.], 2007. http://diglib.uni-magdeburg.de/Dissertationen/2007/nikoleynik.htm.

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Mexis, Meletios. „Optoelectronic properties of InAs GaAs columnar quantum dot laser diodes“. Thesis, Cardiff University, 2008. http://orca.cf.ac.uk/54843/.

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In this thesis results are described with the aim of examining the optoelectronic properties of InAs/GaAs columnar quantum-dots and comparing them with those of more conventional self-assembled quantum-dots. The polarisation properties of a set of columnar quantum-dot samples — of varied aspect ratio and In compositional contrast between the rod-shaped dot and the surrounding 2-D layer — are studied. For this investigation a new method to obtain the ratio of the fundamental TE/TM optical response using edge photo-absorption spectroscopy is proposed, which corrects for the polarisation-dependent features of the experimental set-up. The method is verified by application to compressive and tensile strained InGaP quantum well structures, where the results are in agreement with known ratios of the band-edge matrix elements. When applied to columnar quantum-dot samples it is shown that the TE/TM optical response depends on the dot aspect ratio and the In compositional contrast. A polarisation-independent photo-absorption is illustrated for a columnar quantum-dot of an aspect ratio (dot's height over diameter) 3.51:1, which is desired for use in semiconductor optical amplifiers. For the columnar dot of an extremely high aspect ratio, 7.5:1, a room temperature TM-dominant polarisation lasing emission is observed. By studying the Quantum-Confined Stark Effect, a dramatic enhancement of the Stark shift amplitude is shown for columnar quantum-dot samples of an increased dot aspect ratio from 0.63:1 up to 1.12:1, which may have application in optical modulation/switching. For a higher aspect ratio columnar quantum-dot the shift of the band edge of the photo-absorption spectra is reduced dramatically and this has been attributed to an overall effect where the observable shift becomes the result of higher energy transitions, where their oscillator strength change very rapidly within the studied range of field. For the highest aspect ratio dot, i.e. of aspect ratio 10:1, there is no any observable shift.

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金益民. „Optoelectronic properties of the poly(3-hexylthiophene):ZnO nanoparticles composite thin films“. Thesis, 2014. http://ndltd.ncl.edu.tw/handle/30052816894783429162.

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博士
國立彰化師範大學
光電科技研究所
102
In this study, three topics of issue are discussed. In the first experiment, the effects of the incorporation of ZnO nanoparticles into poly(3-hexylthiophene) (P3HT) was investigated. Hall measurements were performed for demonstrating the carrier conduction mechanism. From the experimental results, conductivity proportional to ZnO doping was observed. The improvement of conductivity is considered to mainly come from a mobility enhancement. Hall-effect analysis by using the polaron theory revealed that ZnO doping might lead to an increased spacing between molecules, thus enhancing the carrier mobility. In the second experiment, the ZnO-doped P3HT/n-type Si diode was fabricated. The effect of ZnO doping on the optical and electrical properties of ZnO-doped P3HT/n-type Si diodes was examined. Charge detrapping/trapping phenomena are studied through time domain measurement for P3HT-based diodes and thin-film transistors. ZnO influences the photoresponse by providing additional holes that serve to reduce the photocurrent time constant. In the third experiment, the ZnO-doped P3HT/Si nanowire arrays/n-type Si diode was fabricated. This is because of SiNWs having a more significant contribution to light injection. The effect of ZnO doping on the optical and electrical properties of ZnO-doped P3HT/Si nanowire arrays/n-type Si diodes was examined.

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Chih-HsuehLan und 藍志學. „Optoelectronic Properties of III-NitrideSemiconductor“. Thesis, 2011. http://ndltd.ncl.edu.tw/handle/80333670452470328806.

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Chen, Tzung-Te, und 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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39

Chen, Tzung-Te. „Optoelectronic Properties of Semiconductor Nanostructures“. 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-0707200812263000.

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40

Chen, Cheng-Hsin, und 陳政欣. „Optoelectronic Properties of III-Nitride Semiconductors“. Thesis, 2003. http://ndltd.ncl.edu.tw/handle/58653479958427350469.

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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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41

Chang, Hsiu-Ju. „Optoelectronic Properties of III-Nitride Semiconductors“. 2007. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2606200718315900.

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42

Huang, Yuan-Fu, und 黃元甫. „Optoelectronic Properties of Graphene Triple Heterojunction“. Thesis, 2018. http://ndltd.ncl.edu.tw/handle/9rstdy.

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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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43

Wan, De-Hui, und 萬德輝. „Applying nanoparticles to develop specific chemical sensors and optoelectronic devices“. Thesis, 2010. http://ndltd.ncl.edu.tw/handle/10003167104612499183.

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博士
臺灣大學
材料科學與工程學研究所
98
In this thesis, we utilized unique physical (optical, photothermal) and chemical properties (chemical affinity, catalytic) of metal nanoparticles (NPs) to develop specific chemical sensors and optoelectronic devices. In chapters 1-3, we briefly introduce the research background, literature reviews and the experimental details. In chapter 4, we suggest two kinds of metal-NP based chemical sensors on Si or flexible substrates. (i) We describe the optical constants of self-assembled hollow gold nanoparticle (HGN) monolayers determined through spectroscopic ellipsometry (SE). The extinction coefficient (k) curves of the HGN monolayers exhibited strong surface plasmon resonance (SPR) peaks located at wavelengths that followed similar trends to those of the SPR positions of the HGNs in solution. The refractive index (n) curves exhibited an abnormal dispersion that was due to the strong SPR extinction. The values of Δn and kmax both correlated linearly with the particle number densities. From a comparison of the optical constant values of HGNs with those of solid Au nanoparticles (SGNs), we used SE measurements to demonstrate a highly sensitive Si-based chemical sensor. HGNs display a slightly lower value of k at the SPR peak but a much higher sensitivity to changes in the surrounding medium than do SGNs. (ii) We fabricated a flexible SPR-based scattering waveguide-sensor by directly imprinting HGNs and SGNs onto flexible polycarbonate (PC) plates—without any surface modification—using a modified reversal nanoimprint lithography (rNIL) technology. Controlling the imprinting conditions, including temperature and pressure, allowed us to finely adjust the depth of embedded metal NPs and their SPR properties. Consistent with the three dimensional FDTD simulations, experimentally We obtained an almost one order of magnitude enhancement in the scattering signal after transferring the metal NPs from a glass mold to a PC substrate. We attribute this enhanced signal to the particles strong scattering of the guiding-mode waves and the evanescent wave simultaneously. In chapter 5, we suggest three kinds of NPs enhanced optoelectronic devices. (i) We demonstrate a new optical data storage method: photomodification of HGN monolayers induced by one-shot of deep-ultraviolet (DUV) KrF laser recording. A single pulse from a KrF laser heated the HGNs and transformed them from hollow structures to smaller solid spheres. This change in morphology for the HGNs was accompanied by a significant blue-shift of the SPR peak. If this spectral recording technique could be applied onto thin flexible tapes, the recorded data density would increase significantly relative to that of current rigid discs. (ii) We describe the preparation of optimal textured structures on Si surfaces through metal-assisted etching using SGNs as catalysts in HF/H2O2 solution. We obtained uniformly textured Si layers containing cylindrical, conical, and bowl-shaped features. A textured surface possessing close-packed pyramidal features with dimensions on the subwavelength scale exhibited the lowest reflectance (< 3%) over the entire visible and NIR spectrum. This low reflectance arose from the refractive index gradient of the Si surface and light trapping phenomena. (iii) We systematically investigated the phenomenon of light trapping in Si solar cells coated with metal and dielectric nanoparticles. Based on the FDTD simulations, we suspected that SGN arrays could be considered as deficient single-layer antireflection coatings: they could reduce the amount of reflected light, scattering it into the Si substrates, while strongly absorbing incident light in the plasmonic resonance wavelength regime. We obtained strong evidence supporting this hypothesis from our observation that the degree of light trapping in Si solar cells was dramatically suppressed when using the SGN arrays under a variety of low reflection conditions. Therefore, we replaced the SGNs with dielectric NPs, which possess lower extinction coefficients and better antireflection ability. Finally, we used a simple, rapid, and cheap solution-based method to prepare close-packed TiO2 NP films on Si solar cells; these devices exhibited a uniform and remarkable increase (ca. 30%) in their photocurrents.

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44

Chiu, Jiann Jong, und 曲建仲. „Organic Semiconductor Nanostructures and Their Optoelectronic Properties“. Thesis, 2003. http://ndltd.ncl.edu.tw/handle/84831288157159606745.

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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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45

Kuo, Po-Fen, und 郭博棻. „Growth and Optoelectronic Properties of SiCN Nanorods“. Thesis, 2003. http://ndltd.ncl.edu.tw/handle/74131759733476557883.

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碩士
國立臺灣大學
物理學研究所
88
We report here a novel two stage method for the growth of one-dimensional single crystal nanorods, which are comprised of Si, C, and N. The first stage involves high-density nucleation on Si substrate by using electron cyclotron resonance plasma-enhanced chemical vapor deposition ( ECRCVD ), while the second stage involves nanorod growth using microwave plasma-enhanced chemical vapor deposition ( MWCVD ) in order to achieve a high growth rate along a preferred orientation. The high-resolution scanning electron microscopic ( HRSEM ) images show that the nanorods are of 1.0-1.5 µm in length and 10-50 nm in diameter with well-faceted hexagonal cross-section. Both electron diffraction and the lattice images indicate that the rods are single crystals with little evidence of defects. The stoichiometry of the crystal was determined by the energy-dispersive x-ray spectrometer ( EDX ) and the results showed a Si, C, N atomic ratio of 2 : 5 : 3 . X-ray diffraction spectroscopy ( XRD ) and x-ray photon spectroscopy ( XPS ) were employed for structural and chemical bonding investigation. Preliminary optical and electronic properties determined by photoluminescence spectroscopy ( PL ), piezo-reflectance spectroscopy ( PzR ) and electron field emission measurement show promising potential for blue-UV opto-electronic and flat panel display applications.

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46

Chang, S. W., und 張尚文. „Growth and optoelectronic properties of SiCN nanostructures“. Thesis, 2000. http://ndltd.ncl.edu.tw/handle/60801162703961536078.

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碩士
國立臺灣大學
物理學研究所
88
In this thesis, an innovative two-stage growth strategy will be presented for the growth of SiCN nanorods and nanowires. In the first stage, an electron cyclotron resonance chemical vapor deposition (ECR-CVD) method was employed to deposit nano-crystalline SiCN buffer layers with various densities on silicon substrates. In the second stage, SiCN nanorods and nanowires were grown rapidly and anisotropically in a microwave plasma enhanced chemical vapor deposition (MW-PECVD) The density of the nanorods or nanowires were determined by the density of the nanocrystals in the buffer layer. The morphology of the nanorods are hexagonal solid rods with diameters of 10 ~ 60 nm and lengths of 1 ~ 1.5 m, while nanowires have diameters of 8 ~ 60 nm and lengths of 4 ~ 6 m. XRD and HRTEM analyses indicated that the structure of the nanorods was close to that of -Si3N4. The EDS (energy dispersive X-ray) and XPS (X-ray photo-electron spectroscopy) confirmed the these nano-structures were composed of silicon, carbon and nitrogen. PL (photoluminescence) and PzR (piezoelectric reflectance spectroscopy) were adapted to measure the optical properties of nanorods and the result showed that a broad direct band gap at 4.2 eV was obtained. The field emission properties of the nanorods are very promising. The emission current could be raised to 4.5 mA/cm2 under in applied external electrical field of 36.7 V/m. This material has a high potential for the blue or UV optoelectronic and field emission display (FED) applications.

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47

Huang, Kuan-Lin, und 黃冠霖. „Optoelectronic Properties of Free-Standing InGaN Membranes“. Thesis, 2015. http://ndltd.ncl.edu.tw/handle/54161441798079208387.

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碩士
國立中興大學
材料科學與工程學系所
103
In this thesis, sacrificial layer is embedded under the 300 nm-thick light emitting diode device with top ITO/Ti/Au thin film deposited on the wafer to protect device. After the electrochemical wet etching, nano-membrane LED are not subject to vertical etching and dramatically increased the lateral etching rate to 250 μm/min. In electrochemical wet etching process, the mechanical stress of ITO/Ti/Au protective layer not only crack the (101 ̅1 ̅) hexagonal pyramid structure but also enhanced the lateral etching rate. In addition to the hexagonal pyramid structure, the surface roughness quite flat (Rms under 2 nm). NM-LED is bending downward direction after lift off. Because MQW is squeezed by lateral lattice, the NM-LED quantum well band is more inclined than ST-LED. The NM-LED PL wavelength is redshift about 1 nm compared with ST-LED. After annealing 600℃ 15 minutes, NM-LED bent downward causing MQW stretched by vertical lattice structure. The PL wavelength of NM-LED blueshift about 2 nm compared with ST-LED. In plane strain extension, PL wavelength is blueshift by changing the amount of deformation. EL of the NM-LED under driving current 0.5 mA, the wavelength redshift about 3.75 nm compared with ST-LED.

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48

Kuo, Po Fen, und 郭博棻. „Growth and Optoelectronic Properties of SiCN Nanorods“. Thesis, 2003. http://ndltd.ncl.edu.tw/handle/10396862516590100996.

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碩士
國立臺灣大學
物理學研究所
91
We report here a novel two stage method for the growth of one-dimensional single crystal nanorods, which are comprised of Si, C, and N. The first stage involves high-density nucleation on Si substrate by using electron cyclotron resonance plasma assisted chemical vapor deposition ( ECRCVD ), while the second stage involves nanorod growth using microwave plasma enhanced chemical vapor deposition ( MWCVD ) in order to achieve a high growth rate along a preferred orientation. The high-resolution scanning electron microscopic ( HRSEM ) images show that the nanorods are of 1.0-1.5 µm in length and 10-50 nm in diameter with well-faceted hexagonal cross-section. Both electron diffraction and the lattice images indicated that the rods are single crystals with little evidence of defects. The stoichiometry of the crystal was determined by the energy-dispersive x-ray spectrometer ( EDX ) and the results showed a Si, C, N atomic ratio of 2 : 5 : 3 . X-ray diffraction spectroscopy ( XRD ) and x-ray photon spectroscopy ( XPS ) were employed for structural and chemical bonding investigation. Preliminary optical and electronic properties determined by photoluminescence spectroscopy ( PL ), piezo-reflectance spectroscopy ( PzR ) and electron field emission measurement show promising potential for blue-UV opto-electronic and flat panel display applications.

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49

Lai, Yu-Sheng, und 賴郁昇. „Structure and optoelectronic properties of semiconductor CuFeO2“. Thesis, 2014. http://ndltd.ncl.edu.tw/handle/13975215638936846270.

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碩士
亞洲大學
光電與通訊學系
102
This study is focused on the crystal structure, cross-sectional microstructure and optoelectronic properties of p-type semiconductor CuFeO2 films. The films were prepared by using sol-gel method and spin-coating, and then annealing under an argon atmosphere. After annealing at 600 and 620◦C,films adopted mixed CuO and CuFe2O4 phases. The 640◦C -annealed material was pure phase CuFeO2. The root mean square roughness increased with the annealing temperature, and 700◦C -annealed film had a higher value of 15.9 nm. Cross-sectional microstructure images were used to analyze the oxide thicknesses. The film material thicknesses were approximate 110~ 130 nm.CuFeO2 is a wide band gap semiconductor that exhibits transparency over the visible wavelength range. These films are p-type semiconductor material, in which had a lowest resistivity of 2.6 Ω cm.

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50

Li, Chia-Wei, und 李家偉. „Synthesis and Optoelectronic Properties of Hyperbranched Polyfluorenes“. Thesis, 2007. http://ndltd.ncl.edu.tw/handle/09218288582519406356.

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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.

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Dissertationen zum Thema „Optoelectronic properties of nanoparticles“

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