Theoretical investigations of adsorption behavior on GaAs(001) surfaces

Adsorption behavior an GaAs(001)-(2 x 4)beta 2 and -c(4 x 4) surfaces is systematically investigated by the calculation of migration potentials for Ga adatoms and Monte Carlo simulation. In the calculation procedure, we use an energy formalism based on the empirical interatomic potentials and the electron counting model in order to incorporate the strain and electronic energy contributions. The calculated migration potentials for Ga adatoms imply that Ga adatoms preferentially reside in missing dimer sites on both (2 x 4)beta 2 and c(4 x 1) surfaces. On the (2 x 4)beta 2 surface, lattice sites in the missing dimer row near As-dimer kinks and B-type step edges are stable for Ga adatoms, whereas no preferential adsorption site is found near A-type step edges. Opposite qualitative trends are found in the migration potentials near step edges on the c(4 x 4) surface. The calculated results are consistent with experimental results and are discussed in terms of atomic configurations and the number of electrons remaining in Ga dangling bonds. Based on the energy formalism, an electron counting Monte Carlo (ECMC) simulation was performed to investigate the adsorption or desorption sequences on GaAs(001)-(2 x 4)beta 2 and -c(4 x 4) surfaces in MBE growth. The results imply that Ga adatoms impinging on the GaAs(001) surfaces play an important role in the incorporation or desorption of As to restore the electron counting model.