Halide perovskites have attracted the attention of a broad segment of the optoelectronics field, owing to their outstanding optical and electrical properties; simple low-temperature solution processing; low-cost raw materials; and tunable bandgaps. The main objective of this dissertation is engineering the materials’ properties of halide perovskites – their crystallinity, composition, and dimensionality – in order to understand the fundamental photophysical processes leading to their extraordinary behavior and to translate this understanding into optoelectronic applications. This dissertation is divided into two parts: the first focuses primarily on halide perovskites as a photonic source from an emission perspective, whereas the second is devoted to fundamental investigation of emergent photophysical concepts in halide perovskite materials including photon recycling and hot carriers. In the first part of this dissertation, we studied the synthesis and characterization of Cs-Pb-Br-based perovskite-related single crystals to elucidate the origin of the materials’ emission properties. After that, we presented perovskite nanocrystals (NCs) as a color converter in solid state lighting and visible light communication. Perovskites NCs’ converted white light (with a high color rendering index of 89 and a color correlated temperature of 3236 K) exhibits an extraordinary modulation bandwidth of 491 MHz, and data transmission rate of 2 Gbit/s. In the second part of this dissertation, we developed a facile synthesis method for perovskite microwires and demonstrate efficient photon recycling in those microwires with conclusive spectroscopic evidence. Subsequently, we investigated hot charge carriers in halide perovskites solar cells by a combination of laser spectroscopy and density functional modelling. Furthermore, we presented that hot holes were extracted at the device interface between the perovskite absorber and a hole transport layer. The findings and methodologies described in this dissertation represent a significant advance for utilizing the optical properties of halide perovskites, bring new fundamental photophysical insights to the field of halide perovskites, and provide a new powerful approach for designing the interface of perovskite solar cells to efficiently extract the hot charge carriers.

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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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最近社會對計算密集型應用程序和高性能的多核計算系統的研究興趣增加。隨著每片芯片和計算資源的核心數量不斷增長的趨勢，更好的金屬互連或其他替代是至關重要的。這亦要滿足高帶寬，低功耗，細小體積和高擴展性的要求。ITRS的報告指出，兼容CMOS的矽光子光互連是一種替代，它符合上述要求，包括體積細少和只需納秒的開關時間，所以矽微環諧振器是具潛能被用為2×2開關元件來建立大規模集成光互連。 / 然而，微環互連的可擴展性可能受限制的，其中四個關注點包括總功耗，插入損耗，光功率不均勻和總串擾。2×2切換微環需要一定的功耗，而插入損耗也限制了每條切換路徑所經過的開關元件的數量。換句話說，開關元件在交互/直行狀態下的非相等損失限制了光互連的可擴展性。此外，在考慮滿足大型光互連的要求，光功率的不均勻性是一個重要的問題。最後，在每個2×2開關元件，輸出光功率洩漏對大型的光互連的輸出造成許多可能的串擾。這在輸出端口的總串擾是十分嚴重，它會減少微環互連的可擴展性。因此，本論文的目的著重於降低整體功耗，路徑的總插入損耗，每個輸出端口的光功率不均勻和每個輸出端口的總串擾。 / 在這篇論文中，我們首先回顧微環諧振器的結構和微環互連的背景。限制互連的可擴展性也將被討論。然後，我們將回顧以前的研究，致力於解決可擴展性問題。通過利用微環開關元件的不相等特徵，我們提出一個有效的模型以找到最佳的開關配置，來減少總功耗和每通道的平均插入損耗。此外，我們還提出一個快速的算法，以較短的計算時間減少交叉狀態開關元件數量。 / There is an increasing research interest on networks-on-chip architectures for growing computation-intensive applications and high-performance multi-core computing systems recently. With the growing trend of number of cores per chip and computation resources per chip, the advancement for conventional interconnections is essential to meet the demands of high-bandwidth capacity, low power consumption, compact footprint and high scalability. A report from ITRS pointed out that optical interconnections based on Complementary Metal Oxide Semiconductor (CMOS)-compatible silicon photonics is an alternative to conform to the above requirements. The carrier-injection-based silicon microring resonators is a promising candidate to build large-scale-integrated optical interconnections using 2×2 switching elements due to its very compact footprint and potential sub-nanosecond switching time. / However, the scalability of microring-based interconnection is limited by issues including power consumption, insertion loss, nonuniformity and crosstalk. Current technology for a 2×2 switching elements of microring requires non-negligible power consumption at cross/bar states on average. Intrinsic insertion loss also limits the number of successive switching elements per switching path. In other words, asymmetric loss characteristics of switching elements limit the scalability of optical interconnections. Also, the nonuniformity of optical power is an important issue to be considered in meeting the requirement of a large-scale optical interconnection. Last, as in each 2×2 switching element, there is an optical power leakage to the non-intended output-port and thus it creates many possible crosstalk powers at each output-port. This total crosstalk at output is severe and needs to be reduced for the scalability consideration of microring-based interconnection. Hence, the aim of this thesis focuses on the reduction in overall power consumption, average total insertion loss per path, average nonuniformity of optical power and total crosstalk at each output-port. / In this thesis we firstly review the background of microring resonator architecture and microring-based interconnections. The severe asymmetric behaviors limiting the scalability of interconnection are discussed. Then we review previous work dedicated to the scalability issues. By leveraging the asymmetric characteristics at cross/bar states of microring switching elements, we then propose an efficient model to find the optimum switching configuration for minimizing the total power consumption and the average insertion loss per path. Heuristics is also proposed to minimize the number of cross state switching elements with a shorter computation time. The results depict that the optimum average total insertion loss per path using 2B-SE achieve a 3.65-dB improvement for 128×128 switch size. The optimum average total insertion loss using 2B-SE in the worst-cast path is shown to be 7.2 dB less than the baseline values without optimization. Furthermore, simulation results show that regarding the nonuniformity in the worst case of the worst case, with the optimum switching configuration, the best improvement is 9.6 dB; the average improvement is 8.7 dB and the least improvement is 7.2 dB for 128×128 switch size. On the other hand, for the total crosstalk per path, simulation results show that the optimum switching configuration can achieve a 1.87-dB improvement for 128×128 switch size on average, compared with the average case without optimization. Also, the total crosstalk has a 2.43-dB improvement for 128×128 switch size in the worst case. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Yuen, Piu Hung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 48-51). / Abstracts also in Chinese. / Acknowledgement --- p.i / Abstract --- p.ii / 摘要 --- p.iv / Table of Contents --- p.vi / Table of Figures --- p.viii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Overview of microring resonators and microring-based optical interconnection --- p.2 / Chapter 1.3 --- Asymmetric characteristics of microring switching elements --- p.3 / Chapter 1.4 --- Problem statement --- p.5 / Chapter 1.5 --- Motivation of this thesis --- p.6 / Chapter 1.6 --- Outline of this thesis --- p.7 / Chapter Chapter 2 --- Previous work on optimization of microring-based interconnection --- p.9 / Chapter 2.1 --- Introduction --- p.9 / Chapter 2.2 --- A previous scheme for insertion loss reduction --- p.10 / Chapter 2.3 --- A previous scheme for nonuniformity reduction --- p.12 / Chapter 2.4 --- Prior work on power consumption in optical networks --- p.14 / Chapter 2.5 --- Prior work on crosstalk in optical cross-connect networks --- p.16 / Chapter 2.7 --- Summary --- p.17 / Chapter Chapter 3 --- Optimization scheme of microring-based interconnection configurations for reduction of power consumption and insertion loss --- p.19 / Chapter 3.1 --- Introduction --- p.19 / Chapter 3.2 --- Principle of determining the optimum switching configurations --- p.20 / Chapter 3.2.1 --- Calculations of power consumption and insertion loss --- p.23 / Chapter 3.3 --- Heuristic for reduction of power consumption and insertion loss --- p.24 / Chapter 3.4 --- Simulation results and discussion --- p.27 / Chapter 3.5 --- Summary --- p.32 / Chapter Chapter 4 --- Optimization scheme of microring-based interconnection configurations for the reduction of nonuniformity and crosstalk --- p.33 / Chapter 4.1 --- Introduction --- p.33 / Chapter 4.2 --- Principle of determining the optimum switching configurations --- p.34 / Chapter 4.2.1 --- Calculation of nonuniformity --- p.35 / Chapter 4.2.2 --- Calculation of crosstalk --- p.36 / Chapter 4.3 --- Simulation results and discussion --- p.39 / Chapter 4.4 --- Summary --- p.42 / Chapter Chapter 5 --- Conclusion and Future Work --- p.44 / Chapter 5.1 --- Conclusion of this thesis --- p.44 / Chapter 5.2 --- Future work --- p.46 / List of Publications --- p.47 / Bibliography --- p.48

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 60-66). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: limiting amplifier; optic receiver; shunt peaking; transimpedance amplifier. Includes bibliographical references (p. 97-100).

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