Impurity bands

This chapter consists of two sections, the first being a description of the concept of impurity band and the phenomena of impurity conduction characteristic of the impurity band. In connection with the analysis of impurity conduction, the historical development of localization theory to the scaling theory is surveyed. The second section offers a review of the current status of theoretical investigations for the interplay between disorder and electron-electron interaction in the impurity bands of doped semiconductors. The present description is limited to the insulating (Anderson-localized) regime of doped semiconductors. A theoretical formulation is developed starting from the intrastate interaction theory, and the effects of the interstate interactions are described. The roles of electron-electron interaction in the specific heat and magnetic properties at low temperatures are clarified and theoretical results are compared with the experimental data on phosphorus-doped silicon. Effects of electronelectron interaction on transport properties and polarizability in the presence of magnetic fields are discussed, and theoretical results are compared with observed magnetoresistance and magnetocapacitance