Low-temperature tunneling spectroscopy ofGe(111)c(2×8)surfaces

Abstract

Scanning tunneling spectroscopy is used to study p-type Ge(111)c(8 2 ×) sur faces 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 1 0 5 0. . ± eV separating the bulk valence band from the surface adatom band is deduced. Peak positions of adatom states are located at energies of eV 02 0 09 0. . ± and eV 03 0 24 0. . ± 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 tipsemiconductor 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 eV 0. 1 ≈ 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.

Structure and electronic spectroscopy of steps on GaAs(110) surfaces

“…Nonequilibrium carrier occupation on the surface has been observed in prior STM/S studies, 16,17,18,19,20 and reduced κ values have been associated with this effect. 19,20 For the present situation, at negative sample voltages, the Fermi-energy at the surface will intersect the states induced by the compensating defects.…”

“…Hence, compared to equilibrium occupation, there will be additional positive charge along the step edge [the model used here is very similar to that previously discussed for defects along surface domain boundaries on Ge (111)c2×8 surface]. 18 This positive change will produce additional downwards band bending, hence reducing the current and producing less-than-ideal κ values. We do not attempt more detailed modeling of the spectra, but qualitatively at least, we believe that these effects can account for the discrepancy we find between the theory and experiment at negative voltages.…”

Electronic states of chemically treated SiC surfaces

“…(It should be noted that for the large band gap of SiC, current flow between conduction and valence bands, i.e. semiconductor inversion, is negligible for the voltages considered here [12]). …”

Charge transfer between isomer domains on n+-doped Si(111)-2 × 1: energetic stabilization

“…With these domains present on the n-type Si surface, charge transfer between bulk and surface is computed by a three-dimensional solution of Poisson's equation including occupation of bulk and surface states in accordance with a fixed Fermi-level F E . Arbitrary energy distributions and spatial arrangements of the surface states, ) ( F i E σ for the i th spatial region, can be easily handled in the finitedifference computation [13,14]; the electrostatic potential is obtained self-consistently with the spatially varying occupation of the surface states in a semiclassical approximation, i.e. with surface state density given by…”

“…Transfer of electrons from the CB to the empty surface-state band is then considered, with the electrostatic potential computed by a finite-difference method previously described [13,14]. 4 The first entry of Table II shows the resulting change in electronic energy at temperature of 8 K for a 10×10 nm 2 positive-isomer domain, computed according to Eq.…”