Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph. D. in Environmental Science)--Vanderbilt University, Aug. 2007. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains viii, 139 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 107-108).

The ever-increasing demand for superior devices with a smaller footprint in electronics calls for research on novel materials as a potential replacement of or integration to the existing silicon-based technology. The emergence of two-dimensional semiconductors paved a promising path in this direction. Easy isolation of atomically thin and flat layers with dangling bond free surfaces enables these materials to not only form 2D vertical heterostructures with novel properties but also facilitates advanced transistor, diode, and tunnel-device design with characteristics such as unprecedented gate-control of the channel, extremely high mobility of charge carriers, high current density, and high on-off ratios. However, like any other technology at the early development phase, 2D semiconductor research also faces numerous challenges which are needed to be addressed. In this work, we address two such challenges in the field–modeling of vertical electrostatics in these complex novel devices which enables better understanding and prediction of their characteristics and overcoming the contact resistance issue in a promising 2D semiconductor, WSe2, which enables the advancement of these devices towards near-deal characteristics. To predict and analyze the electrical characteristics of 2D vertical heterostructures, we need to develop solid understanding of the potential landscape, charge distribution, and energy band diagrams in these devices. Conventional modeling approaches and simulation tools that have been used so far to simulate the transport characteristics obscure our intuition as the devices get more arbitrary and complex. Here, we developed a circuit equivalent model to simulate the vertical electrostatics in these novel and arbitrary heterostructures in a simple and intuitive manner. In our model, all the parameters of the energy band diagram are represented by equivalent circuit elements involving capacitors and voltage sources. We also provide an elegant approach to solve these circuits by using Gauss law in electrostatics and charge-neutrality conditions in quasi-equilibrium. With a computationally efficient algorithm developed to solve these structures, we further built an opensource tool 2dmatstack on nanohub.org that enables researchers to predict and analyze the characteristics of novel heterostructures to maximize research output. In the next section, we focus on a major bottleneck in realizing these vertical devices experimentally. Fermi-level pinning and process-induced surface damage cause large Schottky barriers between metal contacts and these ultrathin 2D semiconducting layers resulting in large contact resistance and poor, non-ideal device performance. The solution to this problem is much more developed in the most widely studied n-type candidate, MoS2, compared to the common the p-type candidate, WSe2. In this work, we develop a UV-ozone-based oxidation technique that transforms the top layer of WSe2 into a nonstoichiometric oxide, TOS, that degenerately dopes the layers underneath p-type. This high hole-doping decreases the Schottky barrier width at the contacts and has resulted in the lowest p-type contact resistance to ultrathin WSe2 reported thus far. We show that this doping is stable in the ambient, remains active at low temperatures, repeatable, robust, and area selective for contact-doping without altering the channel properties. The high-performance ohmic contacts we demonstrate not only sets us in the path to realize near-ideal channel-dominated devices but also is pivotal to understand these devices better by eliminating the effect of contacts from the gate-controlled channel characteristics.

No description available.

The nonlinear optical properties of a semiconductor-doped glass (SDG) channel waveguide were measured on a picosecond time-scale; namely, fluence-dependent changes in the absorption and the refractive index as well as the relaxation time of the nonlinearity. Slower, thermally-induced changes in the refractive index were also observed. The saturation of the changes in the absorption and the refractive index with increasing optical fluence is explained using a plasma model with bandfilling as the dominant mechanism. The fast relaxation time of the excited electron-hole plasma (20 ps) is explained using a surface-state recombination model. A figure of merit for a nonlinear directional coupler fabricated in a material with a saturable nonlinear refractive index is presented. The measured nonlinear change in the refractive index of the SDG saturates below the value required to effect fluence-dependent switching in a nonlinear directional coupler. Experiments with a channel-waveguide directional coupler support this prediction. However, absorption switching due to differential saturation of the absorption in the two arms of the directional coupler was observed.

by Mok Wing Keung. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 149-154). / Acknowledgement --- p.i / Abstract --- p.ii / Table Of Contents --- p.iii / List Of Figures --- p.v / List Of Tables --- p.ix / List Of Plates --- p.x / Chapter Chapter One --- Introduction / Chapter 1.1 --- General introduction --- p.1 / Chapter 1.2 --- Gallium arsenide --- p.4 / Chapter 1.2.1 --- Basic facts --- p.4 / Chapter 1.2.2 --- Band structure --- p.6 / Chapter 1.2.3 --- Production of GaAs --- p.9 / Chapter 1.3 --- Ion implantation --- p.11 / Chapter 1.3.1 --- Principle of ion implantation --- p.11 / Chapter 1.3.2 --- Basic facts --- p.17 / Chapter 1.3.3 --- Radiation damage and annealing --- p.21 / Chapter 1.4 --- Optical measurements --- p.27 / Chapter 1.4.1 --- Basic facts --- p.27 / Chapter 1.4.2 --- Optical reflectance --- p.29 / Chapter 1.4.3 --- Oxide overlayer --- p.39 / Chapter Chapter Two --- Experimental / Chapter 2.1 --- Sample preparation --- p.42 / Chapter 2.2 --- Ion implantation --- p.46 / Chapter 2.2.1 --- Implantation parameters --- p.46 / Chapter 2.2.2 --- Computer modeling of implantation profiles --- p.48 / Chapter 2.3 --- Annealing --- p.57 / Chapter 2.3.1 --- Conventional annealing --- p.57 / Chapter 2.3.2 --- Rapid thermal annealing --- p.61 / Chapter 2.4 --- Optical reflectance measurement --- p.69 / Chapter 2.4.1 --- Principle of measurement --- p.69 / Chapter 2.4.1.1 --- Relative reflectance measurement --- p.71 / Chapter 2.4.1.2 --- Absolute reflectance measurement --- p.79 / Chapter 2.4.2 --- Error estimation and data reduction --- p.82 / Chapter 2.4.2.1 --- Error estimation --- p.84 / Chapter 2.4.2.2 --- Data reduction --- p.86 / Chapter 2.5 --- Optical microscopy and photoluminescence --- p.90 / Chapter Chapter Three --- Results And Discussion / Chapter 3.1 --- Surface morphology --- p.93 / Chapter 3.2 --- Optical reflectance measurement --- p.101 / Chapter 3.2.1 --- Reflectance spectrum --- p.101 / Chapter 3.2.1.1 --- Reference mirror --- p.101 / Chapter 3.2.1.2 --- Crystalline GaAs --- p.104 / Chapter 3.2.1.3 --- Implanted GaAs before annealing --- p.108 / Chapter 3.2.1.4 --- Conventional annealed GaAs --- p.115 / Chapter 3.2.1.5 --- Rapid thermal annealed GaAs (proximity) --- p.120 / Chapter 3.2.2 --- Extraction of optical constants --- p.128 / Chapter 3.2.2.1 --- Oxide overlayer --- p.128 / Chapter 3.2.2.2 --- Dielectric function --- p.132 / Chapter 3.3 --- Photoluminescence results --- p.143 / Chapter Chapter Four --- Conclusions And Suggestions For Further Work --- p.147 / References --- p.149

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Paolo Rava. / Ph.D.

by Chan Kwok Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 93-95). / ACKNOWLEDGEMENT --- p.i / ABSTRACT --- p.ii / LIST OF SYMBOLS --- p.iii / LIST OF FIGURES --- p.v / LIST OF TABLES --- p.vi / Chapter CHAPTER ONE --- INTRODUCTION --- p.1 / Chapter CHAPTER TWO --- SURVEYS ON ION IMPLANTATION DAMAGE STUDY --- p.6 / Chapter 2.1 --- Introduction --- p.6 / Chapter 2.1.1 --- Basic Theory --- p.7 / Chapter 2.1.2 --- Amorphization --- p.9 / Chapter 2.1.3 --- Amorphous Layer Regrowth --- p.10 / Chapter 2.1.4 --- Point Defect Sources --- p.11 / Chapter 2.1.5 --- Types of Extended Defects --- p.11 / Chapter 2.2 --- Nature of Point Defects --- p.15 / Chapter 2.2.1 --- Important Parameters --- p.15 / Chapter 2.2.2 --- Vacancy Centers in Semiconductor --- p.16 / Chapter 2.2.3 --- Self-interstitial in Silicon --- p.17 / Chapter 2.2.4 --- Distribution of Excess Point Defects --- p.18 / Chapter 2.2.5 --- Energy Level of Defect Species --- p.19 / Chapter CHAPTER THREE --- EXPERIMENTAL METHOD --- p.21 / Chapter 3.1 --- Experimental --- p.21 / Chapter 3.2 --- Spreading Resistance Profiling --- p.25 / Chapter CHAPTER FOUR --- MODELING OF SPREADING RESISTANCE PROFILES OF ION-IMPLANTED DAMAGE IN SILICON --- p.29 / Chapter 4.1 --- Introduction --- p.29 / Chapter 4.2 --- Basic equation --- p.30 / Chapter 4.3 --- Formation of Model --- p.34 / Chapter CHAPTER FIVE --- RESULTS AND DISCUSSION --- p.37 / Chapter 5.1 --- Results --- p.37 / Chapter 5.2 --- Discussion --- p.55 / Chapter CHAPTER SIX --- CONCLUSION AND SUGGESTIONS OF FURTHER WORK --- p.58 / Chapter 6.1 --- Conclusion --- p.58 / Chapter 6.2 --- Suggestions of further work --- p.59 / APPENDIX A --- p.60 / APPENDIX B / SPREADING RESISTIVITY PROFILES --- p.62 / REFERENCE --- p.93

ETH, Diss.--Zürich, 2007.