Electron Transport and Trapping at Metal and Oxide Interfaces with Silicon Carbide

Abstract

To continue to drive performance, the next generations of power semiconductor devices need to explore alternative materials other than silicon. The most promising semiconductor for this is silicon carbide (SiC), owing to its superior physical and electrical properties, while also still being compatible with many existing silicon fabrication techniques. SiC Schottky diodes and SiC metal-oxide-semiconductor field-effect transistors (MOSFET) are available commercially, but they have yet to reach theoretical performances. Many existing challenges are related to questions regarding electron transport mechanisms in metal–SiC interfaces, and electron trapping effects in both metal–SiC and oxide–SiC interfaces. This thesis is divided into three parts, and each part addresses one of these areas. In Part I, I investigate electron trapping effects in metal–SiC interfaces (Schottky diodes). Chapter 1 reviews how these traps can impact the device characteristics and reduce device reliability. Chapter 2 experimentally investigates the SiC Schottky diode reliability concerns and provides evidence that they are caused by trap effects. Following this, Part II discusses electron transport at metal–SiC interfaces. Chapters 3 and 4 focus on modelling the current-voltage characteristics of SiC Schottky diodes, both as a means of determining the fundamental current mechanisms and also to build a compact model which can be used in circuit simulations. In chapter 5 I develop a neural network model which can predict the specific contact resistance of SiC Ohmic contacts, using details about the anode metal, the doping, and annealing schedule. Then, chapter 6 contains theoretical advancements in the field of modelling current conduction through defects. Finally, Part III investigates electron trapping in SiC MOS structures. In both chapters 7 and 8 I analyse a specific conductance signal, which has been correlated with lower than theoretical mobilities in SiC MOSFETs. My work illuminates what the cause of this signal is and introduces a new technique to characterize it. Overall, the work contained in this thesis covers a broad range of subtopics in the field of SiC devices. Each of the chapters contained within either contributes to our understanding of the physics of SiC interfaces, and/or improves our ability to engineer high quality SiC devices.