Electron Counting Monte Carlo Simulation of the Structural Change of the GaAs(001)-c(4×4) Surface during Ga Predeposition

An electron counting Monte Carlo (ECMC) simulation is performed to investigate the structural change of As-rich GaAs(001)-c(4×4) surfaces during Ga predeposition, incorporating the As desorption process as a function of Ga adatom coverage based on ab initio calculations. The ECMC simulation results indicate that predepositing 0.5 monolayers of Ga on the GaAs(001)-c(4×4) surface induces As desorption and reduces effective As coverage θ_As to 1.25, where four Ga dimers and two As dimers co-exist in the (4×4) surface unit cell used in this simulation. Subsequent equilibration of this surface changes its structure to (2×4)-like surface with θ_As=0.75 and one As-dimer row and three missing As-dimer rows. These simulated results successfully give one possible interpretation to some puzzling questions in experimental results.