Introduction

Interfaces between semiconductors and metals, insulators, or other semiconductors play an important role in almost all semiconductor devices. This chapter briefly outlines the long and thorny path to a physical understanding of the electronic properties of all these semiconductor interfaces. Exactly 150 years ago, Braun (1874) first reported on the rectifying behavior of metal-semiconductor contacts, and it took until 1938 for Schottky to finally explain this already industrially used observation by depletion layers on the semiconductor side of the interfaces, and then again until 1965 when Heine proposed interface-induced gap states to explain the alignment of the electronic band-structure at both metal-semiconductor and semiconductor-semiconductor interfaces.