Electron states in heavily doped semiconductors

Abstract

Electron states in heavily doped, uncompensated n-type semiconductors are studied in a range of impurity concentrations that cover the non-metallic phase, the metal to non-metal transition, and the high density metallic phase. The non-metallic phase is considered in terms of bound impurity states, dielectrically screened by surrounding impurity states and the host material. For the metallic phase it is assumed that the electrons occupy the host conduction band. The critical concentration for the metal to non-metal transition is determined from considerations of the total energy. For a number of different systems, doped Ge, Si, CdS and InSb, the agreement with experiments is good. For the metallic phase also the extrinsic specific heat and the spin susceptibility have been evaluated. An enhancement has been found in both cases, but the need for a better treatment of the induced charge around the impurities is pointed out in the case of the spin susceptibility. Finally, the combined effect of electron correlation and disorder is discussed to some extent.