Three- to two-dimensional transition in electrostatic screening of point charges at semiconductor surfaces studied by scanning tunneling microscopy

Abstract

The electrostatic screening of localized electric charges on semiconductor surfaces is investigated quantitatively by statistically analyzing the spatial distribution of thermally formed positively charged anion surface vacancies on GaAs and InP͑110͒ surfaces. Two screening regimes are found: at low vacancy concentrations the vacancy charges are found to be three-dimensionally screened by bulk charge carriers. The corresponding screening length, which increases strongly with decreasing carrier concentration, is best described by the classical bulk screening length evaluated with a surface dielectric constant. With increasing vacancy concentration at given bulk carrier concentration, a three-to two-dimensional screening transition occurs. At high vacancy concentrations, the screening is found to be governed by charge carriers located in a two-dimensional surface vacancy defect band, which is partially filled due to the vacancy-induced surface band bending.

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.…”

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

“…The frequently assumed proportionality of the corrugation changes and the potential is not valid, as demonstrated in Ref. 26. Quantitative potential measurements rely on a statistical analysis of interacting charged defects, 19,20,26 the band edge determination in tunneling spectra, 4,14 a work function measurement, or surface photo voltage measurements.…”

“…26. Quantitative potential measurements rely on a statistical analysis of interacting charged defects, 19,20,26 the band edge determination in tunneling spectra, 4,14 a work function measurement, or surface photo voltage measurements. 27 However, in the latter two cases, the tip-induced band bending severely affects the results by shifting the band edges.…”