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

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 (NP) 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 (P) 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.