Temperature-Dependent Electrical Characteristics of β-Ga2O3 Diodes with W Schottky Contacts up to 500°C

Abstract

There is a rapidly growing need for high performance power switching semiconductors in applications such as renewable energy systems, smart grids, transportation electrification, electric and hybrid electric vehicles, industrial machinery control, electricity production, and military systems. Interest in even more efficient, lightweight, and reliable power converters, based on ultra-wide-bandgap (WBG) semiconductors has led to Ga2O3 drawing significant attention due to its large breakdown field of around 8 MV.cm-1. Switches fabricated from wide bandgap semiconductors such as Ga2O3 have a higher power density, better efficiency, and thermal tolerance compared to Si, which can reduce the need for expensive bulky cooling systems. A major drawback of Ga2O3 is its low thermal conductivity. Thermally stable Schottky contacts for these rectifiers are also needed to ensure stability in power conversion systems. In this study, we have measured the electrical characteristics of sputter-deposited W Schottky contacts with Au overlayers for reducing sheet resistance on n-type Ga2O3 before and after device operation up to 500°C. Assuming thermionic emission is dominant, the extracted barrier height decreases with measurement temperature from 0.97 eV (25°C) to 0.39 eV (500°C) while showing little change from its initial value of 0.97 eV after cooling down from each respective operation temperature. The room temperature value is comparable to that obtained by determining the energy difference between binding energy of the Ga 3d core level and the valence band of the Ga2O3 when W is present, 0.80 ± 0.2 eV in this case. The Richardson constant was 54.05 A.cm-2.K-2 for W and the effective Schottky barrier height at zero bias (eΦb0) was 0.92 eV from temperature-dependent current-voltage characteristics. The temperature coefficient for reverse breakdown voltage was 0.16 V/K for W/Au and 0.12 V/K for Ni/Au. The W-based contacts are more thermally stable than conventional Ni-based Schottkies on Ga2O3 but do have more reverse leakage current at higher operating temperatures.