An ab initio-based approach to phase diagram calculations for GaAs(0 0 1)-(2 × 4)γ surfaces

Surface phase diagram of recently proposed GaAs(0 0 1)-(2 × 4)γ is systematically investigated by using our ab initio-based approach. We focus on the (4 × 7) domain consisting of c(4 × 4)-like and (2 × 4)-like regions to clarify surface dimer constituents as functions of temperature T and As (As2 and As4) pressure pAs by comparing chemical potentials of surface dimers in the vapor phase with that on the surface. The calculated results under As4 imply that Ga dimers in the c(4 × 4)-like region tend to become stable with increase of temperature and appear at the conventional growth condition such as T ∼ 800 K and pAs ∼ 10−6 Torr, while the (2 × 4)-like region favors As dimers. This is consistent with temperature dependence of change in surface dimer constituents on the c(4 × 4) and (2 × 4)β2 clarified in our previous study. Furthermore, the surface phase transition from the c(4 × 4) to (2 × 4)β2 via (2 × 4)γ is discussed on the basis of the phase diagram obtained in this study.