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

The surface kinetics of GaAs (001) 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 (001) surface were estimated to be 2 x 10(-6) and 1.5 x 10(-7) cm(2)/s at 530 degrees 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 [110] direction than in the [<(1)over bar 10>] direction. The 2D nucleus size anisotropy is primarily due to a ratio in the lateral sticking probability between steps along the [<(1)over bar 10>] direction (A steps) and steps along the [110] 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 x 10(2) times larger than that at the ascending steps.