Adsorbate-induced Surface States and Fermi-level Pinning at Semiconductor Surfaces

Abstract

Adatoms on semiconductors are inducing surface states and surface dipoles. For the observation of adatom-induced surface states, cleaved surfaces of III-V compound semiconductors are especially suited since they contain no intrinsic surface states within the bulk band gap. At such surfaces, the bands are thus flat up to the surface and adsorbate-induced surface band-bending is thus easily attributed to extrinsic surface states. Such adatom-induced surface states are responsible for the pinning of the Fermi level at adsorbate-covered semiconductor surfaces. Adatom-induced surface dipoles, on the other hand, are changing the ionization energy of the surface. Variations of the work function, finally, are including both changes of the surface band-bending and of the ionization energy.