Bond-angle relaxation and electronic structure of Si and Ge overlayers on (110) surfaces of III–V semiconductors

Abstract

We present the results of a detailed study of relaxational and electronic properties of Si and Ge overlayers on nonpolar (110) surfaces of GaP, GaAs and GaSb. Systems ranging from one up to three homopolar monolayers on semi-infinite heteropolar substrates have been investigated. Structure optimizations, restricted to relaxational degrees of freedom of the overlayer system give rise to a “pseudoionic” outermost adlayer. This pseudoionicity is induced by the adlayer relaxation and by the heteropolarity of the substrates and it leads to pronounced splittings of the Ge and Si surface dangling bond bands similar to the anion- and cation-derived dangling bond bands of the clean relaxed substrate surfaces. Considering the surface layer relaxation asymmetry as a function of overlayer thickness, we find that three monolayers of adatoms are sufficient to decouple the surface from the interface in the overlayer systems. The total energy minimization and electronic structure calculations are carried out in the framework of a second-nearest neighbour empirical tight-binding model. The semi-infinite configurations are treated by scattering theory using one-particle Green functions.