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 potenti als for Ga adatoms and Monte Carlo simulation. In the calculation proc edure, we use an energy formalism based on the empirical interatomic p otentials and the electron counting model in order to incorporate the strain and electronic energy contributions. The calculated migration p otentials for Ga adatoms imply that Ga adatoms preferentially reside i n 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, where as no preferential adsorption site is found near A-type step edges. Op posite qualitative trends are found in the migration potentials near s tep edges on the c(4 x 4) surface. The calculated results are consiste nt with experimental results and are discussed in terms of atomic conf igurations 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 gr owth. The results imply that Ga adatoms impinging on the GaAs(001) sur faces play an important role in the incorporation or desorption of As to restore the electron counting model.