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.