Change in the electronic properties of an InAs (111)A surface at oxygen and fluorine adsorption

Based on ab initio calculations, the adsorption of oxygen and fluorine on reconstructed (2 $\times$ 2) and unreconstructed (1 $\times$ 1) InAs (111)A surfaces is studied. The most stable adsorption positions are determined. It is shown that adsorption of oxygen on both surfaces gives rise to electronic states in the band gap. The preferential positions for oxygen adsorption on an InAs (111)A (2 $\times$ 2) surface are those where oxygen is bonded both to indium atoms and to arsenic atoms in the surface layer and also the vacant site between three indium atoms (the “In-hollow position”). Adsorption of fluorine brings about a pushing of the surface states out of the band gap; the position above indium atoms (the “In-top position”) is preferential for adsorbed fluorine. Adsorption of fluorine on an InAs (111)A (1 $\times$ 1) surface leads to the elimination of the surface state formed by indium $p$ orbitals and to an unpinning of the Fermi level.