Optimization of UV-assisted wet oxidation of GaAs

Abstract

Ultraviolet (UV) light-assisted wet oxidation in deionized water (photowashing) was done on commercial semi-insulating (SI) and N-type (Nd ∼ 7.5 × 1017 cm−3) (100) GaAs substrates. Oxidation rate, depth elemental composition profiling, and structural quality of prepared oxide layers and oxide/GaAs interfaces were evaluated for various oxidation times and for four selected intensities of UV light (320–480 nm) irradiation by means of x-ray reflectivity, x-ray photoelectron spectroscopy, and transmission electron microscopy (TEM), respectively. N-type GaAs exhibited ∼30% higher oxidation rates as compared to SI GaAs. Oxidized layers were found to consist predominantly of Ga2O3. Peak gallium concentrations in oxidized layers related to Ga2O3 achieved ∼45 at. %, while concentrations of arsenic related to unfavorable As2O3 were found to be as low as 4–5 and 4–6 at. % for SI GaAs and N-type GaAs, respectively. As2O3 occurrence was not spatially confined and occurred throughout the oxidized layer. Arsenic depth concentration profiling showed no notable humps suggesting arsenic pile-up at the oxide/GaAs interface. TEM revealed strong correlation between UV light intensity and oxide/GaAs interface roughness. Inhomogeneous oxide layers, rough oxide/GaAs interface, and dislocation formation under excessive UV light intensity were observed. Optimized conditions were found to produce homogeneous oxide layers with smooth oxide/GaAs interface.