Origin of the time dependence of wet oxidation of AlGaAs

The time dependence of the wet oxidation of high-Al-content AlGaAs can be e ither linear, indicating reaction-rate limitation, or parabolic, indicating diffusion-limited rates. The transition from linear to parabolic time depe ndence can be explained by the increased rate of the formation of intermedi ate As2O3 versus its reduction to elemental As. A steadily increasing thick ness of the As2O3-containing region at the oxidation front will shift the p rocess from the linear to the parabolic regime. This shift from reaction-ra te limited (linear) to diffusion-limited (parabolic) time dependence is fav ored by increasing temperature or increasing Al mole fraction. (C) 1999 Ame rican Institute of Physics. [S0003-6951(99)01527-2].