AB-INITIO CALCULATION OF THE ATOMIC AND ELECTRONIC-STRUCTURE FOR SB ADSORBED ON GAAS(110)

We report results obtained by a systematic study of Sb adsorption on t he relaxed GaAs(110) surface, using density-functional theory within t he local-density approximation (LDA) and norm-conserving, fully separa ble, ab-initio pseudopotentials. The GaAs(110) surface is simulated by a slab geometry wherein the atomic structure of the Sb atoms at the p referred adsorption positions and the uppermost substrate layer is opt imized by minimizing the total energy, in contrast to previously repor ted theoretical approaches obtaining the surface bandstructure for giv en geometrical equilibrium structures. Sb coverages of THETA = 1/2 and THETA = 1 are considered. We give a detailed analysis of the total-en ergy surface of the Sb/GaAs(110) system and identify stable and metast able adsorption sites. The resulting equilibrium geometries are discus sed: We interpret these results in terms of the Sb-Sb interaction with in the chains parallel to the [111BAR] direction and of possible struc tural instabilities in such chains. The atomic positions are compared with results of LEED analysis, stating an overall agreement except the buckling of the chain atoms. The resulting electronic properties (sur face bandstructure, photothreshold, Schottky barrier) are discussed wi thin the context of experimental data available from STM, photoemissio n spectroscopy, etc.