Electron States and Elementary Excitations at Semiconductor Surfaces Controlled by Adsorption

Abstract

Adsorption on a doped semiconductor surface often induces a gradual formation of a carrier-depletion or carrieraccumulation layer at the surface, which has a great influence on the surface electronic excitations often coupled with surface optical phonons in compound semiconductors. Firstly, we give a brief survey of formation of depletion layers at ntype GaAs and InSb surfaces and of accumulation layers at n-type InAs surfaces. Secondly, we describe how the subband structure varies in an accumulation-layer formation process at an n-type InAs(110) surface, with special emphasis on the growing influence of nonparabolicity of the conduction-band dispersion. Finally, we elucidate the evolution of surface elementary excitations, namely, two coupled plasmon-phonon modes at the surface and a surface optical-phonon mode involving screening charges, in a depletion-layer formation process at an n-type GaAs(110) surface. Our systematic analysis provides a clear explanation of the change in the electron energy-loss spectrum.