The structure and composition of the (001) surface was studied by means of high-resolution medium-energy ion scattering from As-rich or Ga-rich reconstructions. In contrast to existing models, it was found that the first and second layers of the surface could contain both Ga and As atoms. The surfaces were more Ga-rich than previously thought; with Ga atoms occupying As sites. These mixed compositions were explained in terms of charge neutrality and Coulomb repulsion between surface electrons.

J.Falta, R.M.Tromp, M.Copel, G.D.Pettit, P.D.Kirchner: Physical Review Letters, 1992, 69[21], 3068-71