An ab initio-based approach to Ga adatom migration on GaAs(n 1 1)A-(0 0 1) non-planar surfaces

The behavior of Ga adatoms on GaAs(n 1 1)A (n = 2, 3, 4), (0 0 1)-(2 × 4)β2 and non-planar surfaces consisting of the (2 1 1)A and (0 0 1) are systematically investigated by ab initio-based approach and the Monte Carlo (MC) method. The ab initio total energy calculations clarify strong dependence of Ga adsorption energies on the surface index. Comparing these adsorption energies of Ga with the Ga chemical potentials in the vapor phase, Ga atoms predominantly adsorb on the (2 1 1)A and (3 1 1)A surfaces at high temperatures even beyond ∼1100 K. On the other hand, Ga atoms tend to desorb from the (4 1 1)A and (0 0 1) surfaces at the high temperatures. Furthermore, the MC simulations reveal that diffusion coefficient of Ga adatoms across the (0 0 1) surface is larger than that on the (2 1 1)A surface. This is because Ga migration potential energies on the (0 0 1) surface are smaller than those on the (2 1 1)A surface. Reflecting these results, Ga adatoms on the (2 1 1)A-(0 0 1) non-planar surface migrate on the (2 1 1)A side surface beyond ∼1100 K, whereas Ga adatoms mainly diffuse across the (0 0 1) surface below ∼1100 K.