Introduction

Abstract

The remarkable electronic and structural properties of semiconductor surfaces and interfaces result from the existence of surface and interface states, respectively. Surface states on clean surfaces originate from dangling bonds and on adsorbate-covered surfaces from bonds between adsorbate and semiconductor-surface atoms. At abrupt metal-semiconductor interfaces, the wavefunctions of those metal electrons, which energetically overlap the semiconductor band gap, decay exponentially into the semiconductor. These tails represent metal-induced interface states. This concept also applies to semiconductor heterostructures and semiconductor-insulator interfaces. Surface and interface states above the bulk valence-band maximum may become charged. Surface charge neutrality then requires the existence of space-charge layers which penetrate from the surface or interface into the semiconductor.