A review is presented of the various theoretical methods that have thus far been developed for the study of states introduced by impurities and other point defects in semiconductors. The main body of the paper is prefaced with brief sections on the role of impurities and defects in semiconductors and on the general aspects of experimental techniques, as an appropriate setting for the theoretical discourse. Theoretical methods, including those of the effective-mass type, and a wide range of methods appropriate to deep levels are then presented. Applications of these methods are discussed critically. Finally, the relative merits of the various approaches are compared and the prospects for future work are assessed.

DOI:https://doi.org/10.1103/RevModPhys.50.797