Band gap of the Ge(111)c(2×8) surface by scanning tunneling spectroscopy

The surface band gap of the Ge(111)c(2×8) surface at low temperature is determined on the basis of scanning tunneling spectroscopy. Electrostatic potential computations permit evaluation of tip-induced band bending, from which a correction to the energy scale of the observed spectra is made. Parameter values in the computations are constrained by comparison of the observed spectrum with known spectral features, including high-lying conduction band features derived from first-principles computations. The surface band gap, lying between the bulk valence band maximum and the minimum of an adatom-induced surface band, is found to have a width of 0.49±0.03 eV.