Optical studies of the effect of oxidation on GaN

Optical studies are reported of GaN following oxide layer growth using thermal oxidation and atomic layer deposition (ALD). The low-temperature photoluminescence (PL) probes the topmost GaN layer (<100 nm) where any influence from the oxide is expected. Thermal oxidation results in a 6 meV blue shift of the main PL band (3.478 eV) that is attributed to stress due to formation of GaON/β-Ga₂O₃ upon the GaN surface. A weak PL feature at ∼3.38 eV is due to diffusion of oxygen into the GaN. The Al₂O₃ deposited by ALD does not result in the 3.38 eV band following deposition and subsequent annealing. In contrast, HfO₂ deposited by ALD results in sub-band gap features, which strengthen upon annealing. No appreciable stress is observed for either oxide deposited using ALD, which are not expected to produce GaON/β-Ga₂O₃ layer.