Evolution of electron states at a narrow-gap semiconductor surface in an accumulation-layer formation process

Abstract

Adsorption on a doped semiconductor surface often induces a gradual formation of a carrier-accumulation layer at the surface. Taking full account of a nonparabolic ͑NP͒ conduction-band dispersion of a narrow-gap semiconductor, such as InAs and InSb, we investigate the evolution of electron states at the surface in an accumulation-layer formation process. The NP conduction band is incorporated into a local-density-functional formalism. We compare the calculated results for the NP dispersion with those for the parabolic ͑P͒ dispersion with the band-edge effective mass. With increase in the accumulated carrier density N S , the accumulated carriers for the NP conduction band start to be more localized in closer vicinity to the surface than those for the P one. As the bottoms of a few lowest subbands drop below the Fermi level one after another with increase in N S , the nonparabolicity begins to have a great influence on the dispersion and the bottom of each of these subbands, particularly on those of the lowest subband. The present work provides a numerical basis for making a quantitative examination of surface electronic excitations in the accumulation-layer formation process.

Effect of a skin-deep surface zone on the formation of a two-dimensional electron gas at a semiconductor surface

“…It is also interesting to note that for shallow subbands, located less than 0.1 eV below E F , corrections to their minimal energies resulting from allowing different values of λ are not large, see Table II. Therefore our results agree with earlier calculations by Abe et al [62], referring to such shallow subbands, despite the fact that the specific surface boundary condition, corresponding here to λ → ∞, has been only considered by Abe et al…”

Accurate evaluation of subband structure in a carrier accumulation layer at an n-type InAs surface: LDF calculation combined with high-resolution photoelectron spectroscopy

“…Details of our framework and of our model are described in Ref. 34. We adopt slab geometry to make it easier to obtain a self-consistent solution.…”

“…However, this work was only weakly correlated with the experiment, and restricted to a smaller N s range. 34 In this work, by combining the above LDF calculation with the UPS experiment, we make an accurate evaluation of the subband structure, especially the accumulated-carrier density, the subbandedge energies, and the subband energy dispersion. This analysis follows the accumulation-layer formation process up to such a large N s range as to reveal that the subband dispersion (particularly the lowest-subband one) varies significantly in this process, and that this variation has a considerable influence on collective excitations in the subband.…”

“…This nonparabolicity exerts a remarkable influence on the subband dispersion in the accumulation layer as well. 34 Electric currents or collective electronic excitations in the accumulation layer can be ascribed to free carriers in the subbands. To analyze these phenomena quantitatively, we have to make an accurate evaluation of the subband dispersion, especially around the Fermi level.…”

“…34 We employ the conduction-band dispersion that can be obtained by the k · p method including the spin-orbit splitting. 35 Our previous work on the carrier-accumulation layer at the InAs surface elucidated the nonparabolicity effect on the subbands.…”