Surface kinetics of metalorganic vapor-phase epitaxy: surface diffusion, nucleus formation, sticking at steps

Abstract The surface kinetics of GaAs (0 0 1) surfaces during metalorganic vapor-phase epitaxy (MOVPE) has been investigated quantitatively from high-vacuum scanning tunneling microscopy (STM) images of two-dimensional (2D) nuclei and denuded zones. STM observation was achieved by As passivation of grown-sample surfaces in a vacuum chamber directly connected to an MOVPE system. From 2D-nucleus densities of GaAs and AlAs, the surface diffusion coefficients of Ga and Al species on a GaAs (0 0 1) surface were estimated to be 2 × 10−6 and 1.5 × 10−7 cm2/s at 530°C, and the energy barriers for migration were estimated to be 0.62 and 0.8 eV, respectively. The 2D-nucleus size was 1.5–2 times larger in the [ 1 1 0] direction than in the [1 1 0] direction. The 2D-nucleus size anisotropy is primarily due to a ratio in the lateral sticking probability between steps along the [1 1 0] direction (A steps) and steps along the [ 1 1 0] direction (B steps) (more than 2.5 ± 0.5 : 1). Denuded zones on upper terraces were 2 ± 0.5 times wider than those on lower terraces. This showed that the lateral sticking probability at the descending steps was 10−3 × 102 times larger than that at the ascending steps.