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)b2 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)b2 structures with Ga–As surface dimers. The conventional (2 4)b2 surface consisting of As dimers finally appears due to destabilization of Ga–As dimers at high temperature and high pressure