Electronic states of chemically treated SiC surfaces

Abstract

Electronic states at chemically treated SiC surfaces have been studied by scanning tunneling spectroscopy. Charge accumulation on the surface is deduced through a voltage shift observed in the spectra. More charge is observed on electro-polished surfaces as compared to untreated (as-received) surfaces. This difference is interpreted in terms of the electro-polished SiC surfaces being more insulating than as-received ones, such that on the former the transport of charge is limited and surface charges cannot come into equilibrium with the bulk semiconductor. Observations of tunneling spectra on SiC prepared by various amounts of hydrogen-etching are used to support this interpretation.

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.…”

“…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. Transport through these states (e.g.…”

Oxygen vacancies on SrO-terminatedSrTiO3(001)surfaces studied by scanning tunneling spectroscopy

“…Z(V) is varied according to a|V| where the constant a is typically 1.5 Å/V, and the experimentally determined value of κ is typically 4.5 nm -1 . (This experimental value is less than an ideal κ of 10 nm -1 , due to effects such as residual surface charging [33,34].) We emphasize that this normalization only affects the extent of the conductance axis in Fig.…”

Topographic and electronic structure of cleaved SrTiO3(001) surfaces

“…13 It is also worth mentioning that, for our uncoated samples, a valence band (VB) edge is completely absent in the spectra for both terminations, for sample voltages as low as -3.0 V. This result is consistent with the prior report of Guisinger et al 8 The absence of the VB edge can be generally attributed to a combined effect of equilibrium tipinduced band bending as well as nonequilibrium band bending resulting from surface charging. 16 It is likely that the latter effect dominates in this case since the bulk conductivity of our samples is not so low (~0.1 ohm -1 cm -1 for the as-received wafers, and probably very much higher following the annealing steps). The situation for surface charging at negative sample voltages would be similar to that described in Fig.…”

“…7 of Ref. [16]: positive surface charge is produced by depletion of the surface donor states, causing a reduction in band bending until flat band conditions are reached. Flat band conditions would be achieved for a sample voltage approximately equal to the band gap.…”