Quantitative determination of local potential values in inhomogeneously doped semiconductors by scanning tunneling microscopy

Abstract

Local potential changes arising from nanoscale three-dimensional spatial fluctuations in the dopant distribution in Zn-doped GaAs were investigated quantitatively by scanning tunneling microscopy and spectroscopy at (110) cleavage surfaces. Tunneling spectra measured in areas with different local doping concentration show apparent shifts of the valence band edge and apparent changes of the band gap. A quantitative analysis, combined with band bending and tunnel current simulations, demonstrates that these effects arise from tip-induced band bending that modulates the real potential changes. It is illustrated how exact potential changes between locally high and low doped areas can be determined. It is found that the local potential fluctuations in three-dimensionally doped semiconductors are approximately one order of magnitude smaller that those observed in two-dimensionally doped semiconductors.

Fermi-level pinning in methylammonium lead iodide perovskites

“…This is expected since on unpinned surfaces, the bandgap of a semiconductor can normally not be resolved due to TIBB. 32 In contrast, a high surface defect density leads to strong Fermi-level pinning, which produces a lower tunneling conductance at small negative voltages. Only when the applied negative voltage is large enough, tunneling from the extended states of the valence band steps in.…”

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

“…A possibility to track the local potential V eff (x,y) within the surface layer is to determine the spatially varying valence band maximum (VBM) [76,77]. Figures 2(a) and 2(b) indeed show that the VB onset varies on the sub-nm length scale.…”

Hydrogen on III-V (110) surfaces: Charge accumulation and STM signatures

“…Again, this weakening is very clear in the H ad + images. These differences are not conclusive, and the experimental images themselves do vary somewhat, [45][46][47][48][49][50][51][52][53][54][55][56][57][58] with others looking more like the simulated vacancy images, but it does seem likely that at least some of the reported images are due to H adsorption, not anion evaporation.…”

“…(Indeed, very similar results have recently been obtained for adsorbed hydrogen on cerium dioxide, which looks in STM just like surface oxygen vacancies. 44 ) Here on the III-V (110) surfaces, the only case that looks significantly different is the (rarely considered experimentally [45][46][47][48][49][50][51][52][53][54][55][56][57][58] ) case of H ad − and V C under negative bias (filled states), where H ad − does not look like V C , but does look somewhat like a native (or other) adatom, Fig. 7.…”

“…59), in contrast to the standard simulated images of V A . The interpretation of these STM images was long controversial, since the experiments [45][46][47][48][49][50][51][52][53][54][55][56][57][58] show the vacancies as symmetric, but theoretical studies [59][60][61][62][63][64] always find them to be Jahn-Teller distorted. The accepted explanation 59 is that thermal flipping between two degenerate Jahn-Teller distorted structures averages out to the symmetric simulated STM image shown in the center-right in Fig.…”