Effects of high temperature annealing on the atomic layer deposited HfO2/β-Ga2O3(010) interface

Abstract

Atomic layer deposited HfO2 is a primary candidate for metal-oxide-semiconductor (MOS) power devices based on the ultra-wide bandgap semiconductor β-Ga2O3. Here, we investigated the thermal stability of this stack. Out-diffusion of gallium into HfO2, measured by secondary ion mass spectroscopy depth profile, was observed after annealing at 900 °C. Electrical characterization of MOS capacitors (MOSCAPs) showed that this diffusion caused a dramatic increase in leakage current. For annealing temperatures between 700 and 850 °C, no significant Ga diffusion into the HfO2 layer was observed. Nonetheless, MOSCAPs made with stacks annealed at 700 °C have significantly higher forward bias leakage compared to as-prepared MOSCAPs. Through photo-assisted capacitance-voltage measurements (C-V), we found that this leakage is due to an increase in interface traps (Dit) lying 0.3-0.9 eV below the conduction band. We thus have identified how thermal treatments influence HfO2/Ga2O3 behavior: for anneals at 700-850 °C, we observe an increase in Dit and leakage, while annealing at >900 °C results in notable Ga out-diffusion and a catastrophic degradation in leakage. This understanding is key to improving the performance and reliability of future β-Ga2O3 MOS power devices.