Local Fermi-level pinning at a single adatom (Cs) or vacancy (As) on a GaAs(110) surface

Abstract

Local surface photovoltage imaging with a scanning tunneling microscope is used to demonstrate two types of local Fermi-level pinning next to a single adsorbate or defect, taking advantage of the tip-induced band bending due to the lack of gap states at clean GaAs͑110͒ surfaces. The pinning energy at a single cesium adatom location was determined to be 0.56Ϯ0.04 eV above the valence-band maximum ͑VBM͒, while for As vacancy, the Fermi level cannot go below the top of a filled surface state, 0.62Ϯ0.04 eV above the VBM.

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.…”

Symmetric Versus Nonsymmetric Structure of the Phosphorus Vacancy on InP(110)

“…Although this seems to favor a symmetric atomic structure, the experimental results could not be matched to results of any of the DFT calculations [5][6][7][8]. Furthermore, scanning tunneling spectroscopy (STS) yielded a local downward band bending of 0.1 eV [1], whereas surface photovoltage measurements found a band bending of 0.53 ± 0.3 eV [9] at the site of the positively charged As vacancy on pdoped GaAs(110) surfaces. Concerning the energy levels, the two different DFT calculations predicted the charge transfer levels (+/0) to be 0.32 eV [2] and 0.1 eV [3], and the lowest Kohn-Sham eigenvalues in the band gap to be 0.73 eV [2] and 0.06 eV [3] above the valence band maximum (VBM).…”

Defects in III-V semiconductor surfaces

“…Therefore there have been a number of attempts to determine the exact energy of these localized defect states. The data exhibited, however, large discrepancies: scanning tunneling spectroscopy measurements yielded a local downward band bending of 0.1 eV for positively charged As vacancies in p-doped GaAs(110) [23], whereas surface photovoltage measurements found a band bending of 0.53 ± 0.03 eV [52] at the site of the As vacancy. Similarly, the results for calculated energy levels deviate: density functional theory (DFT) calculations predicted the chargetransition level (+/0) to be 0.32 eV [35] and 0.1 eV [36], and the lowest Kohn-Sham eigenvalues in the band gap to be 0.73 eV [35] and 0.06 eV [36] above the valence-band maximum.…”