Impurity Bands in Group-IV Semiconductors

In this chapter, we describe how the impurity band in group-IV semiconductors is a fascinating subject in condensed matter physics and it manifests a rich diversified physics. After surveying the transport phenomena in the impurity band, metal-insulator transitions, and historical development of the localization theory, we discuss in particular how the electron-electron interactions play an important role in producing anomalous properties, such as peculiar spin-dependent phenomena in specific heat, spin susceptibility, magnetoresistance, etc., in the Anderson-localized regime just in the insulating side of metal-insulator transitions. The most part of chapter is devoted to explaining the theoretical development to treat the interplay of disorder and electron-electron interactions in the Anderson-localized regime of the impurity band. The readers can learn how these theories decipher the origins of various mysterious phenomena which the impurity band exhibits.