Surface diffusion kinetics of GaAs and AlAs metalorganic vapor-phase epitaxy

We have investigated the surface kinetics during metalorganic vapor-phase epitaxy (MOVPE), using high-vacuum scanning tunneling microscopy (STM) observation of two-dimensional (2D) nuclei and denuded zones. Using Monte Carlo simulations based on the solid-on-solid model, from 2D nucleus densities we estimated the surface diffusion coefficients of GaAs and AlAs to be 2 × 10⁻⁶ and 1.5 × 10⁻⁷ cm²/s at 530°C, and the energy barriers for migration to be 0.62 and 0.8 eV, respectively. The 2D nucleus size in the [110] direction was about two times larger than that in the [10] direction. The size anisotropy is caused primarily by a difference in the lateral sticking probability (P_s) between steps along the [10] direction (A steps) and steps along the [110] direction (B steps). The P_s ratio was estimated to be more than 3:1. Denuded zone widths on upper terraces were 2 ± 0.5 times wider than those on lower terraces. This showed that P_s at descending steps was 10 to 3 × 10² times larger than P_s at ascending steps.