Wet Oxidation in a Square Sandwich Composite 
of GaAs/AlAs/GaAs
Wet oxidation in a square sandwich composite, GaAs/AlAs/GaAs, with varying thickness of the AlAs layer was investigated in a temperature range of 400°C–480°C. At a given temperature and time, the oxidation depth increases with increasing thickness of the AlAs layer. A model based on the boundary layer diffusion in a sandwich composite is used to interpret the thickness effect, and the theoretical predictions are in good agreement with the measured oxidation data. The theory also predicts a value of 0.53 eV  ± 0.03 eV to be the difference in activation energies of water vapor diffusion in the central layer AlAs and the outer layers GaAs in the temperature range studied. Such a difference remains to be verified experimentally.