An introduction to silicon inversion layers

In this article the inversion layer, a gas of electrons (or holes) formed at the surface of p (or n) type silicon by an electric field, is described. Inversion layers are of importance as they form the basic of operation of surface controlled devices such as the metal-oxide-silicon field effect transistor (MOSFET), the metal-nitride-oxide silicon memory transistor (MNOS) and the more recently introduced charge coupled device. At low temperatures the inversion layer is electrically decoupled from the bulk silicon and possesses considerable advantages for the investigation of transport phenomena. These stem from the two dimensional nature of the electron gas imposed by the surface potential well and the direct electrical control of the carrier concentration and Fermi energy. The nature of the Si-SiO2 interface is considered end also some of the experimental methods used for obtaining information about its electronic properties. Both room temperature and low temperature properties of the MOS device are outlined and those areas of research in which it is used as a model system are discussed.