Published in Phys. Rev. B 71, 125316 (2005).

Low-temperature tunneling spectroscopy of Ge(111)c(2x8) surfaces

R. M. Feenstra (a), G. Meyer (b), and K. H. Rieder (c)
(a)Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213
(b)Paul Drude Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany
(c)Institut fuer Experimentalphysik, Freie Universitaet Berlin, Arnimallee 14, 14195 Berlin, Germany


Scanning tunneling spectroscopy is used to study p-type Ge(111)c(2x8) surfaces over the temperature range 7 to 61 K. Surface states arising from adatoms and rest-atoms are observed. With consideration of tip-induced band bending, a surface band gap of 0.5 ± 0.1 eV separating the bulk valence band from the surface adatom band is deduced. Peak positions of adatom states are located at energies of 0.09 ± 0.02 eV and 0.24 ± 0.03 eV above this gap. A spectral feature arising from inversion of the adatom state occupation is also identified. A solution of Poisson's equation for the tip-semiconductor system yields a value for the interband current in agreement with the observations, for an assumed tip radius of 100 nm. The rest-atom spectral peak, observed at approx. 1.0 eV below the valence band maximum, is observed to shift as a function of tunnel current. It is argued that nonequilibrium occupation of disorder-induced surface states produces this shift.

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