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Lai Chun Hei Gary = 錳氧化物-鈮摻雜之鈦酸鍶異構結的輸運特性 / 黎鎮禧. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Lai Chun Hei Gary = Meng yang hua wu-ni shan za zhi tai suan si yi gou jie de shu yun te xing / Li Zhenxi. / Acknowledgement --- p.i / Abstract --- p.ii / 論文摘要 --- p.iv / Table of contents --- p.vi / List of Figures --- p.x / List of Tables --- p.xv / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Introduction to perovskite manganites and niobium doped strontium titanate --- p.1-1 / Chapter 1.1.1 --- Structure and properties of perovskite manganites --- p.1-1 / Chapter 1.1.2 --- Structure and properties of niobium doped strontium titanate --- p.1-4 / Chapter 1.1.3 --- Phase transition in perovskite manganites --- p.1-9 / Chapter 1.1.4 --- Charge ordering and small polaron theory in PCMO --- p.1-15 / Chapter 1.1.5 --- Colossal Magnetoresistance (CMR) in perovskite manganites --- p.1-19 / Chapter 1.16 --- Review of semiconducting junction between perovskite manganites and niobium doped strontium titanate --- p.1-23 / Chapter 1.2 --- Research motivation --- p.1-28 / Chapter 1.3 --- Scope of this thesis --- p.1-29 / References --- p.1-31 / Chapter Chapter 2 --- Experimental details / Chapter 2.1 --- Thin film deposition --- p.2-1 / Chapter 2.1.1 --- Facing-target sputtering --- p.2-1 / Chapter 2.1.2 --- Vacuum system --- p.2-3 / Chapter 2.1.3 --- Fabrication and characterization of manganites targets --- p.2-4 / Chapter 2.1.4 --- Substrate --- p.2-7 / Chapter 2.1.5 --- Deposition procedure --- p.2-8 / Chapter 2.1.6 --- Silver electrode coating apparatus --- p.2-10 / Chapter 2.2 --- Annealing systems --- p.2-12 / Chapter 2.2.1 --- Vacuum annealing system --- p.2-12 / Chapter 2.2.2 --- Oxygen annealing system --- p.2-14 / Chapter 2.3 --- Characterization --- p.2-16 / Chapter 2.3.1 --- Profilometer --- p.2-16 / Chapter 2.3.2 --- X-ray diffractometer --- p.2-16 / Chapter 2.3.3 --- Resistance measurement system --- p.2-18 / Chapter 2.3.4 --- Current-voltage characteristics measurement system --- p.2-20 / References --- p.2-23 / Chapter Chapter 3 --- Epitaxial LCMO/STON heterojunction / Chapter 3.1 --- Four point and two point I-V measurement --- p.3-1 / Chapter 3.2 --- Magnetic phase transition of LCMO revealed by four point I-V measurement of LCMO/STON heteroj unction --- p.3-8 / Chapter 3.3 --- Oxygen annealing effect on LCMO/STON heteroj unction --- p.3-14 / Chapter 3.4 --- Positive colossal Magnetoresistance in LCMO/STON heteroj unction --- p.3-16 / References --- p.3-23 / Chapter Chapter 4 --- Epitaxial PCMO/STON heterojunction / Chapter 4.1 --- Ohmic contact for PCMO thin films --- p.4-1 / Chapter 4.2 --- PCMO charge ordering and magnetic phase transition --- p.4-9 / Chapter 4.3 --- Four point I-V measurement of PCMO/STON heterojunction --- p.4-14 / References --- p.4-16 / Chapter Chapter 5 --- Epitaxial LCMO/PCMO/STON junction / Chapter 5.1 --- Tunneling junction fabrication --- p.5-1 / Chapter 5.2 --- Structural characterizations --- p.5-2 / Chapter 5.3 --- PCMO magnetic phase transition revealed by I-V measurement of LCMO/PCMO/STON tunneling junction --- p.5-3 / Chapter 5.4 --- Energy band structure of perovskite manganites --- p.5-11 / Chapter 5.4.1 --- Introduction to energy band of perovskite manganites and STON --- p.5-11 / Chapter 5.4.2 --- Temperature dependent band structure of LCMO explained by diffusion voltage of LCMO/STON heterojunction --- p.5-18 / References --- p.5-22 / Chapter Chapter 6 --- Conclusions / Chapter 6.1 --- Conclusion --- p.6-1 / Chapter 6.2 --- Future outlook --- p.6-3

Wai, Kwai Fong = 錳氧化物 - 鈮摻雜之鈦酸鍶異構結的電流電壓關係測量 / 韋桂芳. / "Sept 2007." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Wai, Kwai Fong = Meng yang hua wu - ni shan za zhi tai suan si yi gou jie de dian liu dian ya guan xi ce liang / Wei Guifang. / Acknowledgement / Abstract / 論文摘要 / Table of content / List of Figures / List of Tables / Appendix A / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Structure and properties of perovskite manganites / Chapter 1.2 --- Magnetoresistance (MR) / Chapter 1.3 --- Giant Magnetoresistance (GMR) / Chapter 1.4 --- Colossal Magnetoresistance (CMR) / Chapter 1.4.1 --- Exchange interaction and CMR / Chapter 1.5 --- p-n junction / Chapter 1.5.1 --- Fundamentals of a p-n homojunction / Chapter 1.5.2 --- Deviations from the Ideal Diode / Chapter 1.5.2.1 --- Zener breakdown / Chapter 1.5.2.2 --- Avalanche / Chapter 1.5.3 --- Heterojunction / Chapter 1.6 --- Research motivation / Chapter 1.7 --- Scope of the thesis / References / Chapter Chapter 2 --- Experimental details / Chapter 2.1 --- Thin film deposition / Chapter 2.1.1 --- Facing target sputtering / Chapter 2.1.2 --- Vacuum system / Chapter 2.1.3 --- Deposition procedure / Chapter 2.2 --- Oxygen annealing system / Chapter 2.3 --- Silver electrode coating apparatus / Chapter 2.4 --- Characterization / Chapter 2.4.1 --- Alpha-step profilometer / Chapter 2.4.2 --- X-ray diffractometer / Chapter 2.4.3 --- Electrical transport property measurement / Chapter 2.4.3.1 --- Measurement of resistance as a function of temperature (RT) / Chapter 2.4.3.2 --- Measurement of I-V characteristics of a junction / References / Chapter Chapter 3 --- Epitaxial LSMO/STON heterojunction / Chapter 3.1 --- Sample preparation / Chapter 3.2 --- Results and Analysis / Chapter 3.2.1 --- Structural analysis / Chapter 3.2.2 --- R-T measurement / Chapter 3.2.3 --- I-V measurement / Chapter 3.2.3.1 --- Analysis of diffusion voltage and breakdown voltage / Chapter 3.2.3.2 --- Construction of energy band diagram of LSMO/STON at room temperature / Chapter 3.2.3.3 --- Investigating how the energy band structure varies with the temperature / Chapter 3.2.3.4 --- Further development of the energy band analyzing method to wide-p/narrow-n heteroj unction / Chapter 3.2.3.5 --- Forward-biased deviations from ideal / Chapter 3.2.3.6 --- Discussion on the reasons for deviations from ideal / Chapter 3.2.4 --- MR determination / References / Chapter Chapter 4 --- Epitaxial [LSMO/PCMO] multilayers and p-n junction / Chapter 4.1 --- [LSMO/PCMO]/NGO multi-layered thin films / Chapter 4.1.1 --- Sample preparation / Chapter 4.1.2 --- Results and analysis / Chapter 4.1.2.1 --- Structural analysis / Chapter 4.1.2.2 --- R-T measurement / Chapter 4.2 --- [LSMO/PCMO]/STON multi-layered junction / Chapter 4.2.1 --- Sample preparation / Chapter 4.2.2 --- Results and analysis / Chapter 4.2.2.1 --- Structural analysis / Chapter 4.2.2.2 --- R-T measurement / Chapter 4.2.2.3 --- I-V measurement / Chapter 4.2.2.3.1 --- Analysis of diffusion voltage and breakdown voltage / Chapter 4.2.2.3.2 --- Investigating the energy band structure as a function of temperature / Chapter 4.2.2.3.3 --- Forward-biased deviations from an ideal junction diode / Chapter 4.2.2.3.4 --- Review on MR calculation / Chapter 4.2.2.3.5 --- Analysis of MR of [LSMO(8 A ) /PCMO(8 A)]/STON and LSMO/STON / References / Chapter Chapter 5 --- [La0 4Ca0.6MnO3/La0.8Ca0.2MnO3］p-n junction / Chapter 5.1 --- Sample preparation / Chapter 5.2 --- Result and analysis / Chapter 5.2.1 --- Structural analysis / Chapter 5.2.2 --- R-T measurement / Chapter 5.2.3 --- I-V measurement / Chapter 5.2.3.1 --- Analysis of diffusion voltage and breakdown voltage / Chapter 5.2.3.2 --- Investigating the energy band structure as a function of temperature / Chapter 5.2.3.3 --- Forward-biased deviations from ideal / Chapter 5.2.3.4 --- MR analysis / Chapter Chapter 6 --- Conclusion / Chapter 6.1 --- Conclusion / Chapter 6.2 --- Future outlook

In this Ph.D. work, we investigate the optoelectronic properties of low-bandgap semiconducting polymers and project the potential for employing these materials in electronic and photonics devices, with a particular emphasis on use in organic solar cells. The field of organic solar cells is well developed and many of the fundamental aspects of device operation and material requirements have been established. However, there is still more work to be done in order for these devices to ultimately reach their full potential and achieve commercialization. Of immediate concern is the low power conversion efficiency demonstrated in these devices so far. In order to improve upon this efficiency, several routes are being explored. Because the optical bandgaps of semiconducting polymers are larger than in inorganic semiconductors, one of the most promising routes currently under exploration is the development of low-bandgap materials. Using polymers with lower band gaps will allow more of the solar irradiance spectrum to be absorbed and converted into electricity and thus possibly boost the overall efficiency. The bandgap of these semiconducting polymers is determined by the chemical structure, and therefore can be tailored through synthesis if the relevant structure-property relationships are well-understood. The materials studied in this work, a new series of Poly(thienylenevinylene) (PTV) derivatives, posses lower band gaps than conventional polymers through a design that incorporates aromatic-quinoid structural disturbances. This type of chemical structure delocalizes the electronic structure along the polymer backbone and reduces the energy of the lowest excited-state leading to a smaller band-gap. We investigate these materials through a variety of techniques including linear spectroscopy such as absorption and photoluminescence, pump-probe techniques like cw-photoinduced absorption and transient photo-induced absorption, and the non-linear electroasborption technique in order to interrogate the consequences of the delocalized electronic structure and its response to optical stimuli. We additionally consider the effects of environmental factors such as temperature, solvents and chemical doping agents. During the course of these investigations, we consider both of the two primary categorical descriptions of structure-property relationships for polymers within the molecular exciton model, namely the role of inter-molecular interactions on the electronic properties through the variation of supermolecular order and the fundamental determination of electronic structure due to specific intra-molecular interaction along the backbone of the polymer chain. We show that the dilution of aromaticity in semiconducting polymers, while being a viable means of reducing the optical band gap, results in a significant increase in the role of electron-electron interactions in determining the electronic properties. This is observed to be detrimental for device performance as the highly polarizable excited state common to polymers gives way to highly correlated state that extinguishes both the emissive properties and more importantly for solar cells, the charge-generating characteristics. This situation is shown to be predominant regardless of the nature of interchain interactions. We therefore show that the method of obtaining low-bandgap polymers here comes along with costly side-effects that inhibit their efficient application in solar cells. Further, we directly probe the efficacy of these materials in the common bulk-heterojunction architecture with both spectroscopy and device characterization in order to determine the limiting and beneficial factors. We show that, while from the point of view of absorption of solar radiation these low-bandgap polymers are more suited for solar cells, the ability to convert the absorbed photons into electron-hole pairs and generate electricity is lacking, due to the internal conversion into the highly correlated state and thus, the absorbed photon energy is lost. For completeness, we fabricate devices and verify that both the charge-transport properties and alignment of charge extraction levels with those of the contacts can not be responsible for the dramatic decrease in efficiency found from these devices as compared to other higher band gap polymers. We thus conclusively determine that the lack of power converison efficiency is governed by the inefficiency of charge-generation resulting from the intrinsic defective molecular structures rendering a low-lying optically forbidden state below the lowest optical allowed state that consumes the majority of the photogenerated excitons. It is emphasized that our means of investigation allow us to truly access the potential of these materials. In contrast, the direct application of these systems in devices and interpretation of the performance is exceedingly complex and may obscure their true potential. In other words, poor performance from a device may be extrinsic in nature and the optimization process may be very costly with respect to both time and materials. The methods used here however, allow us to determine the intrinsic potential. Not only is this beneficial in terms of preserving the resources that would be used on the trial-and-error method for devices, but it also allows us to learn more on a fundamental level about the structure-property relationships and their implications for device performance. The benefits of this increased understanding are two-fold. First, by learning about the fundamental response of a material, a new application may be realized. For example, the rapidly efficient internal conversion process that renders the materials in this study as poor candidates for solar cells may make them useful for photonics applications, as optical switches, for instance. Secondly, this type of investigation has implications for the whole organic electronics community instead of just being limited to the particular material system and the primary application attempted. In this case, we are essentially able to determine a threshold for aromaticty necessary in a structure that will preserve the stability of the ionic excited state that is useful for charge generation in solar cells.

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

In this work a new current-sweep stress methodology for quantitatively assessing the mixed-mode reliability (simultaneous application of high current and high voltage) of advanced SiGe HBTs is presented. This stress methodology allows one to quickly obtain the complete damage spectrum of a given device from a particular technology platform, enabling better understanding of the complex voltage, current, and temperature interdependence associated with electrical stress and burn-in of advanced transistors. We consistently observed three distinct regions of mixed-mode damage in SiGe HBTs, and find that hot carrier induced damage can be introduced into SiGe HBTs under surprisingly modest mixed-mode stress conditions. For more aggressively scaled silicon-germanium technology generations, a larger percentage of hot carriers generated in the collector-base junction are able to travel to and hence damage the EB spacer, leading to enhanced forward-mode base current leakage under stress. A new self-heating induced mixed-mode annealing effect was observed for the first time under fairly high voltage and current stress conditions, and a new damage mechanism was observed under very high voltage and current conditions. Finally, as an example of the utility of our stress methodology, we quantified the composite mixed-mode damage spectrum of a commercial third-generation (200 GHz) generation SiGe HBT. It is found that if devices are stressed with either voltage or current alone during burn-in, they can easily withstand extreme over-stress conditions. Unfortunately, devices were easily damaged when stressed with a combination of stress voltage and current, and this has significant implications for the device and circuit lifetime prediction under realistic mixed-signal operating conditions.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Cressler, John; Committee Member: Gerhardt, Rosario; Committee Member: Ingram, Mary Ann; Committee Member: Papapolymerou, John; Committee Member: Shen, Shyh-Chiang. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--Ohio University, June, 2004. / Title from PDF t.p. Includes bibliographical references (leaves 62-64).

Thesis (M.Sc.). / Written for the Dept. of Physics. Title from title page of PDF (viewed 2008/12/04). Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 156-165). Available also in a digital version from Dissertation Abstracts.