Semiconductor Interfaces

Abstract

Rectifying metal-semiconductor or Schottky contacts, semiconductor het-erostructures, and semiconductor-insulator interfaces are most important concepts in semiconductor devices and circuits. When two solids are in contact and no intermixing occurs, their electronic structures will be nevertheless perturbed locally at the interface since there the bonding configurations differ from those in the bulk of both materials. The lineup of the electronic band structures at semiconductor interfaces, as different as they seem to be, may be described in one and the same simple model. It considers the tailing of the electron wavefunctions across the interface in the energy range where the metal conduction band overlaps the band gap of the semiconductor or the valence band of one of the semiconductors overlaps the band gap of the other one. In this concept, insulators differ from semiconductors only by their very large band gaps. As the familiar exponential decay of the electron wavefunctions into vacuum at surfaces, the wavefunction tailing at interfaces between solids is also due to the quantum-mechanical tunneling. As surface states on clean and on adatom-covered semiconductor surfaces, these interface-induced gap states derive from the virtual gap states of the complex band structure of the corresponding semiconductor. Tailing of electron wavefunctions means charge transfer across the interface so that generally dipole layers will exist at interfaces as on surfaces.