Tight-Binding Model of Surface Donor-States Induced by Metal Adatoms on GaAs(110) Surfaces

Metals deposited on clean GaAs(110) surfaces held at low temperatures are inducing extrinsic surface states of donor type. For metals with an outer s -electron the energy levels of such surface donors are calculated in a tight-binding model. The approach used describes the adatom-substrate bonding as a diatomic, heteropolar "surface-molecule" in which the metal s -electrons are forming bonds with dangling sp 3 -hybrids of surface Ga-atoms. The chemical trend of the calculated energy of the bonding states as a function of the atomic term values of the metal s -electrons is in agreement with experimental data.