Metal contacts to silicon and indium-phosphide-cleaved surfaces and the influence of intermediate adsorbed layers

Abstract

Detailed studies, using a range of experimental techniques, are described of the interfaces formed between metals and the semiconductors silicon and indium phosphide. For contacts between Ag or Au and cleaved (111) Si the existence of thin adlayers of oxygen or chlorine at the interface makes little difference to the magnitude of the Schottky barrier formed, although the adlayers totally change the electronic structure of the free surface. Au, Ag, and Cu contacts on clean (110) surfaces of InP yield good Schottky barriers but exposure of the clean surface to oxygen, air or chlorine prior to deposition of the metal electrodes leads to low apparent barrier contacts at room temperature. Reactive metals such as Al, Fe, and Ni also yield low barrier contacts, at room temperature, when deposited on clean surfaces of InP. These results coupled with studies on other materials cast some doubt about the usefulness of the quantity S, ’’the index of interface behavior’’ often used to describe metal–semiconductor interfaces and on the existence of the much quoted covalent-ionic transition. The present results on InP may be understood in terms of a defect model and details of this model are discussed. The interface electronic properties are dominated by chemical and metallurgical effects.