Realistic Tight-Binding Calculations of Surface States of Si and Ge (111)

We give semiempirical tight-binding calculations of dangling- and back-bond surface bands and resonances for unreconstructed relaxed Si and Ge (111) surfaces. For Si at high-symmetry points these are in very good agreement with those of Appelbaum and Hamann. Comparison of the results with the energy-loss-spectroscopy data of Rowe and Ibach suggests that the observed back-bond resonances are associated primarily with minima in the back-bond surface bands.