Improved Performance of 4H-SiC PiN Diodes Using a Novel Combined High Temperature Oxidation and Annealing Process

In this paper, the application of a novel combined high temperature thermal oxidation and annealing process to mesa-isolated epitaxial-anode 4H-SiC PiN diodes with thick ( \(110~\mu \) m ) drift regions is presented, the aim of which was to increase the carrier lifetime in the 4H-SiC. Diodes were fabricated using 4H-SiC material having undergone this process, which consisted of a thermal oxidation in dry pure O₂ at 1550°C followed by an argon anneal at the same temperature. Forward current-voltage characterization showed that the oxidised/annealed samples typically showed around 15% lower forward voltage drop and around 40% lower differential on-resistance (at 100 A/cm \(^{2}\) and 25°C) compared to control sample PiN diodes, whilst reverse recovery tests indicated a carrier lifetime increase also of around 40%. These findings illustrate that the use of this process is a highly effective and efficient way of improving the electrical characteristics of high voltage 4H-SiC bipolar devices.

I. Introduction

Of the wide band gap (WBG) materials that are currently being investigated for power electronics applications, 4H-silicon carbide (SiC) technology is the most advanced; this is a result of extensive research over the past twenty five years. However, in recent years, the WBG material gallium nitride (GaN) has seen great improvements in material quality and is a serious contender for future power electronics devices. Although 4H-SiC has a narrower band gap when compared to GaN, its thermal conductivity is vastly superior, making it more suitable for high power density applications, such as high voltage direct current (HVDC) power transmission. Furthermore, because GaN is typically grown on a substrate of different material (such as silicon (Si), sapphire or SiC), only lateral power devices are feasible. This effectively rules out the use of GaN power devices for applications above several kV in voltage, which require the use of vertical device structures with a thick epitaxial blocking layer. Finally, the direct band gap of GaN means it has a very short carrier lifetime, meaning GaN bipolar devices are infeasible. As such, 4H-SiC is widely tipped to be the successor to Si for high voltage power electronics [1].