Electronic properties of Sb deposited on GaAs(110) in the submonolayer coverage regime.

Abstract

We present theoretical calculations of the electronic structure of a Sb/GaAs~110! interface in a submonolayer deposition regime. We have studied two different structural models of the Sb islands on GaAs~110! corresponding to a coverage u50.625. A self-consistent first-principles pseudopotential method using densityfunctional theory within the local-density approximation has been used to calculate the minimum-energy atomic configuration of the Sb islands and of the GaAs substrate. In particular, we have determined the equilibrium geometry and the electronic properties of the Sb terrace edges. The terrace terminated with a Sb atom bonded to an As atom of the substrate is energetically favored with respect to the edge having the Sb atom bonded to a Ga substrate atom. In both cases there is a tendency of the Sb atom on the edge to move towards a site at which a threefold coordination can be reestablished by forming a bond with another atom of the substrate. This is achieved by reducing its height with respect to the substrate plane. The single-particle band structure shows electronic states that fall within the optical band gap. These electronic states are nonbonding dangling bonds of p orbital character strongly localized on the Sb terrace edges. We analyze the electronic charge distribution associated with these states, the features introduced in the density of states and the surface band structure. The results are interpreted in terms of a reorganization of the bonding configuration of the atoms at the terrace edges. Finally, we examine the problem of the discrepancy between our ab initio results predicting metallic interfaces and the experimental outcome showing a semiconducting system, where the electronic states associated with the terrace edges form two peaks, one fully occupied, the other empty, both lying within the optical band gap of the GaAs~110! surface. @S0163-1829~96!08027-7#