Non-damaging growth and band alignment of p-type NiO/β-Ga2O3 heterojunction diodes for high power applications

Abstract

This work fabricated NiO/β-Ga₂O₃ heterojunctions deposited using confined magnetic field-based sputtering at different oxygen flow rates and compared these with a Schottky barrier diode. It is noteworthy that confined magnetic field-based sputtering is considered a less damaging technique compared to other methods. Also, this technique allows for the formation of a stable plasma. First, the optical and electrical properties of the NiO thin film were discussed. We noticed that with increasing oxygen flow rates, the NiO bandgap increased, and resistivity decreased. Furthermore, an XPS technique was used to analyze the chemical state of NiO films at different oxygen flow rates and also to extract a NiO/β-Ga₂O₃ band offset. In addition, we observed that the p-NiO interlayer improved NiO/β-Ga₂O₃ heterojunction performance compared with a Schottky barrier diode. First, the leakage of current was reduced, and breakdown increased from −552 to −644 V after the insertion of a 4.7% NiO interlayer. This improvement was explained by the decrease in interfacial state density. A very low on-resistance (R_on) with a value of 10.85 mΩ cm² was obtained by increasing the O₂/Ar percentage to 10%. Moreover, we noticed that with increasing oxygen flow rate, the on-voltage had two variations, an increase and then a decrease. The increase in V_on is explained by the increasing conduction band with increasing oxygen flow rate, but the decrease is explained by the effect of trap-assisted tunneling transport mechanism activation. These variations were confirmed with a TCAD simulator. Furthermore, with the combination of NiO with the oxygen flow rate of 10% as a top layer and a 4.7% oxygen flow rate as an interlayer for the formation of a NiO(10%)/NiO(4.7%)/β-Ga₂O₃ dual-layer heterojunction, a very low on-resistance of about 10.3 m cm² with a breakdown voltage close to −950 V was obtained. Finally, the reason for low breakdown voltage was analyzed using the Silvaco TCAD simulator. Furthermore, the devices exhibit high thermal stability and can operate at temperatures around 150 °C.