Optical Studies of the Effect of Oxidation on GaN
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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/b-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/b-Ga2O3 layer.