Atomic and electronic structures of GaAs(110) and their alkali-adsorption-induced changes.

Abstract

We performed density-functional-theory total-energy and force calculations of clean and Na-covered GaAs(110) for two coverages: \ensuremath{\Theta}=1/2 (one Na atom per pair of Ga and As) and \ensuremath{\Theta}=1/4. The atomic positions of the adsorbate and of the top three substrate layers are fully relaxed. We discuss the nature of the adsorbate-substrate interaction, the adsorbate-adsorbate interaction, how the adsorbate modifies the clean-surface geometry, and how the atomic and electronic structures are correlated. It is found that the adsorption is partially ionic. The highest occupied adsorbate-induced ``band'' reflects the properties of a Mott-insulator state, where the lowest unoccupied state is a one-dimensional Bloch state.