First-principles study of GaP(0Â 0Â 1) surfaces

First-principles total energy calculations have been performed on GaP(0 0 1) surfaces to determine the disordered structure during phase transitions. The Ga-rich and P-rich (2 × 1), (2 × 2) and (2 × 4) structures were discussed. The surface phase diagram showed that a disordered phase exist during phase transition between (2 × 1) and (2 × 4) structures, which was assigned to be the coexistence of three ordered structures: β2(2 × 4), δ(2 × 4) and Ga(2 × 1)md. This result does not support the observations that the disordered structure is a mixture of α(2 × 4) and β(2 × 4) [D.C. Law, Y. Sun, R.F. Hicks, J. Appl. Phys. 94 (2003) 6175]. Generally, good agreement in structural parameters was obtained with previous results. Total and partial density of states analysis for three stable phases was presented.