Epitaxial growth and semiconductor properties of NiGa2O4 spinel for Ga2O3/NiO interfaces

TL;DR

This study demonstrates the controlled epitaxial growth of NiGa2O4 spinel layers at Ga2O3/NiO interfaces, revealing their structural, optical, and electronic properties, and their potential as p-type interlayers in high-temperature Ga2O3 electronic devices.

Contribution

It provides a systematic method for growing NiGa2O4 layers and characterizes their properties, offering new insights into their role at Ga2O3/NiO interfaces in high-power electronics.

Findings

NiGa2O4 films of 10-50 nm were grown with low surface roughness.

The optical absorption onset varies with substrate temperature.

NiGa2O4/Ga2O3 heterojunctions show high rectification ratios and stability at high temperatures.

Abstract

Unintentionally formed interfacial layers are ubiquitous in semiconductor devices that operate at extreme conditions. However, these layers' structure and properties often remain unknown due to the thinness of these naturally formed interphases. Here, we report on the intentional epitaxial growth and semiconductor properties of NiGa2O4 spinel layers that form at Ga2O3/NiO interfaces used in high-power and high-temperature electronic devices. Cubic spinel NiGa2O4 films of 10-50 nm thicknesses and low surface roughness (~ 2 nm) were grown using pulsed laser deposition at a substrate temperatures in the 300-900 {\deg}C range on {\alpha}-Al2O3 and {\beta}-Ga2O3 substrates of different orientation. The optical absorption onset (3.6-3.9 eV) and thermal conductivity (4-9 W m-1 K-1) vary systematically with substrate temperature, consistent with theoretical predictions of varying Ni and Ga cation ordering on the spinel lattice. The valence band offset between NiGa2O4 and {\beta}-Ga2O3 is determined to be 1.8 eV. The NiGa2O4-based p-n heterojunction devices on Ga2O3 (001) substrates exhibit a rectification ratio of 10^8 (for +/-2V) and a turn-on voltage of 1.4 V, maintaining diode behavior up to 600 {\deg}C. These results highlight the potential of NiGa2O4 as a p-type interlayer in Ga2O3-based devices and shows a new approach to investigate such interfacial layers.