Effects of SiO2 cap annealing on MOS interfaces formed on Mg-doped p-type GaN surface

In this paper, we report the effects of 800 °C SiO2 cap annealing on the Al2O3/p-type GaN (p-GaN):Mg and SiO2/p-GaN:Mg interfaces formed at relatively low temperatures, as determined by X-ray photoelectron spectroscopy (XPS) and sub-bandgap-light-assisted capacitance–voltage (C–V) measurement. For the sample with capless annealing at 800 °C and subsequent HF treatment before the Al2O3/p-GaN interface formation by atomic layer deposition at 300 °C, its C–V characteristics indicated the existence of high-density midgap states. By SiO2 cap annealing and subsequent HF treatment to remove the cap layer, we found that the Al2O3/p-GaN interface showed a reduction in midgap state density. The same effect was confirmed at the SiO2/p-GaN interface. Taking this finding and XPS results together, we consider the possibility that SiO2 cap annealing at 800 °C and the subsequent HF treatment prior to the formation of the Al2O3/p-GaN and SiO2/p-GaN interfaces led to the reduction of interface disorder.