Ho Ming Kei = 新的有機發光器件的界面研究 / 何銘基. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Ho Ming Kei = Xin de you ji fa guang qi jian de jie mian yan jiu / He Mingji. / Abstract --- p.i / 论文摘要 --- p.iii / Acknowledgements --- p.iv / Table of Contents --- p.v / List of Figures --- p.viii / List of Tables --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Overview --- p.1 / Chapter 1.2 --- Conjugated Polymers --- p.2 / Chapter 1.2.1 --- Electronic and geometric Configuration --- p.2 / Chapter 1.2.2 --- Charge Carries of conjugated polymers --- p.4 / Chapter 1.2.3 --- Polymer Light Emitting Diodes --- p.11 / Chapter 1.2.4 --- Device Fabrication --- p.12 / Chapter 1.2.5 --- Polymeric Luminescent Material Development --- p.18 / Chapter 1.2.6 --- Interface and Surface of PLED --- p.21 / Chapter 1.3 --- Aims of this thesis --- p.22 / References --- p.24 / Chapter Chapter 2 --- Instrumentation --- p.26 / Chapter 2.1 --- X-ray Photoelectron Spectroscopy --- p.26 / Chapter 2.1.1 --- Introduction --- p.26 / Chapter 2.1.2 --- Basic Principles and Theory --- p.28 / Chapter 2.1.3 --- Qualitative Analysis Using XPS --- p.29 / Chapter 2.1.4 --- Angular Effect on XPS --- p.29 / Chapter 2.1.5 --- Chemical Shifts --- p.30 / Chapter 2.1.6 --- Quantitative Analysis using XPS --- p.31 / Chapter 2.1.6.1 --- Survey spectrum --- p.32 / Chapter 2.1.6.2 --- Core level spectrum --- p.32 / Chapter 2.1.6.3 --- Valence band spectrum --- p.33 / Chapter 2.1.7 --- Instrumental Setup for XPS --- p.33 / Chapter 2.2 --- HV physical vapor deposition system with nitrogen glove box --- p.36 / Chapter 2.2.1 --- Nitrogen grove box --- p.38 / Chapter 2.2.2 --- HV physical vapor deposition system --- p.38 / Chapter 2.3 --- L-V-I measurement system --- p.41 / Chapter 2.3.1 --- Keithley 236 source-measure unit --- p.41 / Chapter 2.3.2 --- Photo Research PR-650 photo meter --- p.43 / Chapter 2.3.3 --- Test Environment Chamber --- p.43 / Chapter 2.4 --- a-Step Profilometer --- p.44 / References --- p.45 / Chapter Chapter 3 --- Interface study between MEHPPV: PEG and Aluminum --- p.46 / Chapter 3.1 --- Introduction --- p.46 / Chapter 3.2 --- Sample Preparations --- p.47 / Chapter 3.2.1 --- Si(lll) substrate preparation --- p.47 / Chapter 3.2.2 --- Au sputtering on the clean Si Surface --- p.48 / Chapter 3.2.3 --- Polymer film formation --- p.48 / Chapter 3.3 --- Results and Discussion --- p.49 / Chapter 3.3.1 --- XPS Survey scan ofMEHPPV --- p.51 / Chapter 3.3.2 --- XPS of Cls Core level ofMEHPPV --- p.51 / Chapter 3.3.3 --- XPS ofOls Core level ofMEHPPV --- p.55 / Chapter 3.3.4 --- XPS of A12p Core level ofMEHPPV --- p.59 / Chapter 3.3.5 --- XPS Survey scan of PEG --- p.64 / Chapter 3.3.6 --- XPS of Cls Core level of PEG --- p.64 / Chapter 3.3.7 --- XPS of Ols Core level of PEG --- p.67 / Chapter 3.3.8 --- XPS of A12p Core level of PEG --- p.70 / Chapter 3.3.9 --- XPS survey scan of MEHPPV:PEG(10wt% PEG) --- p.73 / Chapter 3.3.10 --- XPS Cls core level of MEHPPV:PEG(10wt% PEG) --- p.73 / Chapter 3.3.11 --- XPS Ols core level of MEHPPV:PEG(10wt% PEG) --- p.76 / Chapter 3.3.12 --- XPS A1 2p core level of MEHPPV: PEG --- p.80 / Chapter 3.3.13 --- Surface migration of bulk absorbed oxygen --- p.84 / Chapter 3.4 --- Conclusions --- p.84 / Reference --- p.87 / Chapter Chapter 4 --- Efficiency enhancement in polymer light emitting diodes using Crown ether 18-C6 and aluminum cathode --- p.89 / Chapter 4.1 --- Introduction --- p.89 / Chapter 4.2 --- Sample preparation --- p.91 / Chapter 4.2.1 --- The Cleaning of substrate --- p.91 / Chapter 4.2.2 --- PEDOT: PSS film formation --- p.93 / Chapter 4.2.3 --- Emissive polymer layer formation --- p.94 / Chapter 4.2.4 --- Deposition of metal cathode --- p.94 / Chapter 4.2.5 --- Epoxy Encapsulation --- p.95 / Chapter 4.3 --- Results and Discussion --- p.95 / References --- p.101 / Chapter Chapter 5 --- Concluding Remarks and Future Work --- p.102 / Chapter 5.1 --- Concluding Remarks --- p.102 / Chapter 5.2 --- Future Work --- p.103

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Solid-state lightings are becoming the popular choice for lightings due to its higher efficiency, improved colour rendering index and the flexibility of various size and shape. Halide perovskite has tunable colour emission, low disorder and is solution processable making it one of a popular choice as emitters. This thesis demonstrates the versatility of using halide perovskite material in light-emitting diodes. We demonstrate the first working perovskite light-emitting diode at room temperature by introducing thin layer of perovskite emitter which is crucial to confine the inherent free carriers in the material. We show that the 3D lead-halide bulk perovskite is bandgap tunable with emission in the green and red visible spectrum. Light-emitting diodes in the visible spectrum are common however near-infrared emission is a rarity. Lead is a heavy metal which is known for its toxicity. We tackled the issue of toxicity by replacing with tin and demonstrate tunable emission in the near-infrared region. Bulk perovskites have large binding energy which makes it difficult to confine the charges and form radiative recombination which is crucial for emission and efficiency of the device. We move into lower dimensionality perovskites by utilising all-inorganic perovskite nanoplatelets and show emission in the blue region.

Lei, Dangyuan = 表面等離子交叉耦合協助氧化鋅發射的理論和實驗研究 / 雷黨願. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 81-85). / Abstracts in English and Chinese. / Lei, Dangyuan = Biao mian deng li zi jiao cha ou he xie zhu yang hua xin fa she de li lun he shi yan yan jiu / Lei Dangyuan. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Motivations --- p.1 / Chapter 1.2 --- Thesis outline --- p.3 / Chapter 2 --- Background and Proposition --- p.7 / Chapter 2.1 --- Surface plasmon mediated emission from semiconductor --- p.7 / Chapter 2.1.1 --- General mechanism --- p.7 / Chapter 2.1.2 --- Formulation of SP coupling --- p.10 / Chapter 2.1.2.1 --- Derivation of dispersion relation --- p.10 / Chapter 2.1.2.2 --- Plasmonic density of states (DOS) --- p.13 / Chapter 2.1.2.3 --- Field distribution in dielectric/metal/dielectric System --- p.13 / Chapter 2.1.2.4 --- Determination of Purcell factor (Fp) --- p.16 / Chapter 2.1.3 --- Emission enhancement from metal-capped ZnO --- p.17 / Chapter 2.2 --- Proposal for making high efficiency top-emitting LED --- p.22 / Chapter 3 --- Experimental Setup and Measurement System --- p.24 / Chapter 3.1 --- Sample preparation --- p.24 / Chapter 3.1.1 --- Radio frequency magnetron sputtering --- p.24 / Chapter 3.1.2 --- Spin-coating --- p.27 / Chapter 3.1.3 --- Rapid thermal annealing --- p.29 / Chapter 3.2 --- Optical characterizations --- p.29 / Chapter 3.2.1 --- Transmittance measurement --- p.29 / Chapter 3.2.2 --- Photoluminescence (PL) measurement --- p.31 / Chapter 3.2.3 --- EDX for composition measurement --- p.32 / Chapter 4 --- Theoretical Simulations and Experimental Results --- p.36 / Chapter 4.1 --- Tunable surface plasmon resonance by using metal alloys --- p.36 / Chapter 4.1.1 --- Dielectric constants calculation --- p.37 / Chapter 4.1.2 --- Dispersion relation of alloy/Si02 --- p.41 / Chapter 4.1.3 --- Plasmonic density of states and Purcell factor of alloy/semiconductor --- p.43 / Chapter 4.1.3.1 --- Air/AlxAg1-x/ZnO system --- p.43 / Chapter 4.1.3.2 --- Air/AlxAul-x/ZnTe --- p.46 / Chapter 4.1.3.3 --- Air/ AgxAul-x/CdSe system --- p.48 / Chapter 4.1.4 --- Experimental results of AlxAgl-x/ZnO --- p.52 / Chapter 4.1.5 --- Discussion and mini-conclusion --- p.56 / Chapter 4.2 --- Enhanced forward emission from metal-insulator-metal/ZnO by coupled surface plasmon --- p.57 / Chapter 4.2.1 --- Plasmon modes in metal-insulator-metal (MIM) --- p.57 / Chapter 4.2.2 --- Transmittance simulation of MIM and MIMIM --- p.63 / Chapter 4.2.3 --- Transmittance measurement of MIM --- p.68 / Chapter 4.2.4 --- Transmittance and photoluminescence of MIM/ZnO. --- p.73 / Chapter 4.2.5 --- Discussion and mini-conclusion --- p.78 / Chapter 5 --- Conclusions --- p.79 / Chapter 6 --- References --- p.81

Quantum Dots (QD) have become a commercial reality for tunable displays and light-emitting diodes. The Department of Energy believes further improvements in efficacy and stability will allow for widespread adoption of solid-state lighting in the United States. QD geometric and compositional architecture, crystal phase and surface chemistry are arguably some of the important aspects governing QD performance in these applications. Chapter I outlines the efforts of QD design, encapsulation and performance for phosphor converted, “on-chip” LEDs. Cadmium chalcogenide QDs with a quantum well geometry and ZnS encapsulation (CdS/CdSxSe1-x/CdS/ZnS) resist photoluminescence bleaching on chip under harsh accelerated ageing tests. Trends in device performance are linked primarily to success of ZnS passivation. Chapter II presents findings regarding crystal structure control (Zinc Blende vs Wurtzite) for CdX (X = S, Se) systems by focusing on crystal phase conversion. The ZB to W transition for CdX is shown to be size, material and surfactant dependent. Chapter III focuses on expanding the precursor compound library for CdSe with aryl substituted cyclic selenones (imidazole and pyrimidine-based compounds). These molecules are shown to react sluggishly at ZB synthetic conditions and that the rate is heavily influenced by compound sterics. Chapter IV presents the findings of a metal carboxylate displacement study on PbS NCs with various L-type ligands. Upon displacement and purification with N,N,N′,N′-tetramethylethylene-1,2-diamine, tri-n-butylamine, and n-octylamine, oriented attachment occurs along the 100 plane and with bis(dimethylphosphino)ethane and tri-n-butylphosphine, attachment is suppressed. This difference allows for the study of ligand density dependent optical properties without the confounding attachment of nanocrystals in solution. A decreasing trend of time resolved photoluminescence lifetime values as a function of ligand density is observed.

This project involved designing and building a radiochromic film (RCF) densitometer using a still digital camera as the light detector and light emitting diode, LED, as the light source. The behaviour of the LED and charged coupled device (CCD) in the still digital camera, under different light exposure settings (by changing LED current and camera shutter speed) were measured and an optimal setting was determined. Additionally, methods were devised and tests were carried out in order to spread the illumination area of the single light source. Uniform spreading of the LED illumination area was possible by the use of two diffusers placed at an optimum separation distance that was determined in this work. The usefulness of this custom-made RCF densitometer was demonstrated by using this device to image exposed RCF and using the film analysis software, Image J, to determine the film absorbed dose. Two clinical situations were examined: open and virtual wedge radiation beams. It was concluded that still digital cameras can be used in RCF densitometers provided they can capture and store raw images, a single diffused LED can illumination an area large enough for RCF densitometry and appropriate film analysis software is needed to extract and handle the large volume of greyscale data from the RCF.

The radiation effects in III-V heterojunction devices are investigated in this thesis. Two types of heterojunction devices studied are InGaP/GaAs single heterojunction bipolar transistors (SHBTs) and GaN-based heterojunction light emitting diodes (LEDs). InGaP/GaAS HBTs are investigated for high energy (67 and 105 MeV) proton irradiation effects while GaN heterojunction LEDs are studied for neutron irradiation effects. A compact model and the parameter extraction procedures for HBTs are developed, and hence the I[subscript C]--V[subscript CE] characteristics of pre- and post-irradiation HBTs can be simulated by employing the developed model. HBTs are electrically characterized before and after proton irradiation. Overall, the studied HBT devices are quite robust against high energy proton irradiation. The most pronounced radiation effect shown in SHBTs is gain degradation. Displacement damage in the bulk of base-emitter space-charge region, leading to excess base current, is the responsible mechanism for the proton-induced gain degradation. The performance degradation depends on the operating current and is generally less at higher currents. Compared to the MBE grown devices, the MOVPE grown HBTs show superior characteristics both in initial performance and in proton irradiation hardness. The 67 MeV protons cause more damage than 105 MeV protons due to their higher value of NIEL (non-ionizing energy loss). The HBT I-V characteristics of pre- and post-irradiated samples can be simulated successfully by employing the developed model. GaN heterojunction LEDs are electrically and optically characterized before and after neutron irradiation. Neutron irradiation causes changes in both the I-V characteristic and the light output. Atomic displacement is responsible for both electrical and optical degradation. Both electrical and optical properties degrade steadily with neutron fluence producing severe degradation after the highest fluence neutron irradiation. The light output degrades by more than 99% after 1.6x10����� n/cm�� neutron irradiation, and the radiation damage depends on the operating current and is generally less at higher currents. / Graduation date: 2003

Recently, the high-power light-emitting diodes (LEDs) have been used from the traditional indicator purpose to general illumination purpose. The operating environment and requirement has been more severe. The long operating life high efficiency and high reliability are its main feature attracting the lighting community to this technology. The effect of operating temperature on the degradations of high-power blue LEDs is studied in this thesis. The experiment, measurements, and finite element simulations were conducted to investigate the possible causes of LED degradation. The influence of LED material degeneration on the radiometric pattern was analyzed by tracing rays simulation. Different groups of sample LEDs produced by Lumileds, Unity opto technology Co., and Everlight electronics Co. were studied. Different operating ambient temperatures, e.g. 80oC, 100 oC, and 120 oC, were considered in the accelerated aging test. Experimental results indicated that yellowing, carbonization, gel degeneration, lens chapping and deformation were observed during the test. Results also indicated that the operating temperature is the key factor for LED failure mechanism, that is, different operating ambient temperature may lead to different degradation phenomenon. Numerical simulation results shown that the creep caused by high temperature and thermal stress would cause solder takeoff. This takeoff defects were observed in experimental results. Through ray tracing simulation, it is assured that gel degeneration would change the radiometric pattern of the LED significantly.

Organic semiconductors have the advantage over traditional inorganic semiconductors, such as Si or GaAs, in that they do not require perfect single crystal films to operate in real devices. Complicated multi-layer structures with nanometer scale thicknesses can thus be easily fabricated from organic materials using low-cost roll-to-roll manufacturing techniques. However, the discrete nature of organic semiconductors also implies that they typically contain almost no intrinsic charge carriers (i.e., electrons or holes), and thus act as insulators until electrical charges are injected into them. In electrical device applications this means that all of the holes and electrons within a device must be injected from the anode and cathode respectively. As a result, device stability, performance, and lifetime are greatly influenced by the interface between the organic materials and the electrode contacts. Despite the fundamental importance of the electrode/organic contacts, much of the basic physical understanding of these interfaces remains unclear. As a result, the current design of state-of-the-art organic optoelectronic devices tends to be based on trial and error experimentation, resulting in overly complicated structures that are less than optimal. In the present thesis, various electrode/organic interfaces relevant to device applications are studied using a variety of different techniques, including photoelectron spectroscopy and the iii temperature dependent current-voltage characteristics of single carrier devices. The fundamental understanding gleaned from these studies has been used to develop new strategies for controlling the energy-level alignment at electrode/organic interfaces. A universal method for tuning the work function of electrode materials using a halogenated organic solvent and UV light has been developed. Application of this technique in organic light emitting diodes enabled the first highly simplified two-layer device with a state-of-the-art record breaking efficiency.