The As and Ga surface coverages of the c(4 x 4), c(2 x 8), (2 x 4), (2 x 6), and c(8 x 2) reconstructions of (001)GaAs were determined by using high-resolution medium-energy ion-scattering methods. It was found that all of the surfaces were more Ga-rich than was predicted by current structural models. The results were explained in terms of charge neutrality and Coulomb repulsion between As lone-pair orbitals, leading to As replacement by Ga in the first and second surface layers.

J.Falta, R.M.Tromp, M.Copel, G.D.Pettit, P.D.Kirchner: Physical Review B, 1993, 48[8], 5282-8