A Monte Carlo simulation study for adatom migration and resultant atomic arrangements in AlxGa1−xAs on a GaAs(001) surface

The Monte Carlo method is applied to investigate adatom migration of cations in AlxGa1−xAs (x = 0, 0.5 and 1.0) and the resultant atomic arrangements on a reconstructed As-stabilized GaAs(001) surface in the adatom coverage range of θ ≤ 0.5. Cation adatom migration strongly depends on the adatom coverage on the surface. Randomly impinging cations occupy lattice sites on the As dimers at the low coverage of θ ≤ 0.1. As the coverage increases in the range of 0.1 < θ ≤ 0.3, impinging cations predominantly migrate along the missing dimer rows. At a higher coverage of θ > 0.3, adatoms tend to favor the lattice sites on the As dimers including those with non-tetrahedral coordination. In Al0.5Ga0.5As, lattice sites along the missing dimer are mainly occupied by Al adatoms, while those on As dimers are favored by Ga adatoms. This is because Al adatom migration proceeds several times more slowly than Ga adatom migration. These resultant atomic arrangements are discussed in terms of the coverage dependence of the migration potential.