STRUCTURE OF IMPURITY BANDS IN LIGHTLY DOPED SEMICONDUCTORS (REVIEW).

A review is provided of recent work on the structure of an impurity band of a compensated semiconductor with such a low donor concentration that the overlap of the wave functions can be ignored. The structure of an impurity band is understood to be the density of states, position of the Fermi level, and spatial distribution of empty and occupied donors at zero temperature. These quantities are found on a computer by direct minimization of the Coulomb energy of the interaction of electrons with one another and with charged impurities. A detailed minimization program is described. It is demonstrated that the density of states near the Fermi level has a Coulomb gap and that in the case of moderate degrees of compensation this gap governs largely the whole density-of-states pattern. Results are given of calculations of the distribution of internal electric fields, activation energy of hopping conduction epsilon //3, temperature dependence of the hopping conductivity with a variable jump length, and impurity-concentration correction to the activation energy of band conduction.