Green's-function studies of Ge adsorption on GaAs(110)

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Abstract
We present the results of a detailed electronic-structure study of submonolayer and monolayer Ge adsorption on the GaAs(110) surface. The calculations have been performed using the tight-binding scattering theoretical method. The formalism as it applies to chemisorption is described and a particularly efficient way for accurately calculating the necessary Green's functions is introduced. On the basis of a model Hamiltonian, we have investigated the electronic properties for a variety of conceivable adsorption geometries. In the case of submonolayer adsorption, we find four salient chemisorption-induced bands whose nature and origin are discussed on the basis of surface band structures and layer densities of states. Our results favor bonding of Ge to the substrate Ga atoms in the unrelaxed surface geometry. The calculated electronic properties of this configuration are in good agreement with experimental data on submonolayer and half-monolayer adsorption systems. In the case of monolayer coverage, the system's electronic structure exhibits bound states and resonances which can clearly be recognized as the immediate precursors of the Ge-GaAs(110) heterojunction interface bands.