Isoelectronic impurities in semiconductors are investigated using a Koster-Slater one-band—one-site approximation. Good agreement with experiment is found for the optical absorption induced by nitrogen in gallium phosphide. Binding energies of excitons to single nitrogen impurities and to double nitrogen impurities are calculated using the complete structure of the GaP conduction bands. Very limited success is achieved in these calculations, which ignore correlation effects and the lattic relaxation and electronic polarization of the host crystal. The indications are that the response of the host to the impurity is of crucial importance in the short-range-interaction problem in semiconductors.

• Received 19 March 1968

DOI:https://doi.org/10.1103/PhysRev.175.991