Theoretical investigation of phase transition on GaAs(0 0 1)-c(4 × 4) surface

The surface phase transition between GaAs(0 0 1)-c(4 × 4) and -(2 × 4)β2 surfaces is systematically investigated by using our ab initio-based approach. The phase diagram calculations for the c(4 × 4) surfaces as functions of temperature and As pressure reveal that three kinds of c(4 × 4) surfaces consisting of Ga-As dimers and/or Ga-Ga dimers become stable near the phase transition temperature. The electron counting Monte Carlo simulation and ab initio calculations are also performed to investigate the structural change of the c(4 × 4) surface after predepositing a 0.5 monolayer of Ga on the three kinds of c(4 × 4) surfaces. The calculated results suggest that the c(4 × 4) surfaces consisting of three Ga-As dimers or one Ga-Ga dimer and two Ga-As dimers in the (4 × 4) surface unit cell possibly change their structures to (2 × 4)β2 structures with Ga-As surface dimers. The conventional (2 × 4)β2 surface consisting of As dimers finally appears due to destabilization of Ga-As dimers at high temperature and high pressure.