Chemistry and kinetics of the GaAs oxidation by plasma anodization: Anin situreal-time ellipsometric study

Abstract

In situ real-time ellipsometry is used to study the GaAs oxidation process by radio-frequency plasma anodization. The effect of the GaAs surface temperature, the bias potential applied to GaAs substrate, the crystallographic orientation, and UV-light irradiation on the chemistry and kinetics of GaAs oxidation are investigated. Oxide layers from tenths to hundreds of angstroms in thickness are grown at temperatures as low as 130 \ifmmode^\circ\else\textdegree\fi{}C and bias voltages ranging between 5 and 50 V. The rate of oxidation is further increased by irradiation of the GaAs surface with UV light during plasma anodization. The role of the diffusion of oxidizing species and of the drift of gallium and arsenic ions on the oxidation kinetics is discussed and the UV photoenhancement effect is clarified. These plasma-grown GaAs oxide layers have a unique composition in that they are almost stoichiometric and contain ${\mathrm{As}}_{2}{\mathrm{O}}_{5}$ as the main arsenic oxide.