Gallium Nitride and Gallium Arsenide Based Devices for Power Switching and Photonics Application
thesisposted on 27.10.2017 by Chenjie Tang
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
Silicon has been dominating semiconductor industry for the past several decades. Even though the performance and cost of Si devices have been significantly improved with innovations in technology, circuit topologies, etc, they are fast approaching the theoretical limitations. III-V compound semiconductors, particularly gallium nitride (GaN) and gallium arsenide (GaAs), are being investigated as potential replacements of Silicon for power switching and photonics applications. However, the development of GaN-based power switching transistors has encountered three major obstacles: current collapse under pulsed condition; limited breakdown voltage and/or high leakage current; lack of cost-efficient method for normally-off operation. The first part of this work studies these issues and presents approaches to address the problems through physics-based TCAD simulations. Current collapse and breakdown mechanisms in E-mode (normally-off) AlGaN/GaN and InAlN/GaN metal-insulator-semiconductor heterostructure field-effect transistors (MISHFETs) have been investigated thoroughly. Current collapse is observed in transient simulations even with highly efficient surface passivation. The influence of buffer traps and passivation layers on current collapse and breakdown voltage of GaN devices have been studied systematically. And several methods are proposed for suppressing current collapse, maintaining low buffer leakage and achieving high breakdown voltage. The second part of this thesis focuses on GaN- and GaAs-based quantum wells for photonics application. High performance photodetectors are designed for infrared and terahertz applications by utilizing intersubband transitions within quantum wells. A three-level AlGaN/GaN step quantum well is studied to obtain a flat potential profile, which enables the transition energy from the ground state to the first excited state to fall into the THz range. And the effects of delta doping location and density on wavelength shifts are investigated by solving Schrödinger-Poisson equations self-consistently. Additionally, a new concept of triple quantum well photodetector is proposed and has been implemented within AlGaAs/GaAs material system to achieve mid-infrared wavelength detection. The photodetector is designed with a unique double-resonance condition with benefits in achieving low noise current, large electron escape probability and high absorption coefficient.