Ga-As intermixing in GaAs(001) reconstructions

Using high-resolution medium-energy ion scattering, we have determined the surface As and Ga coverages of the c(4×4), c(2×8), (2×4), (2×6), and c(8×2) reconstructions of GaAs(001). All surfaces are more Ga rich than predicted by current structural models. The results are 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. © 1993 The American Physical Society.