Green’s function techniques were used to calculate the position of deep defects in narrow-gap semiconductors. In order to predict chemical trends, the effects of various elements were considered. Substitutional (including antisite), (ideal) vacancy, and interstitial (self or foreign) deep defects were examined. The effect of the relaxation of neighbors was considered for the substitutional and interstitial cases. It was noted that relaxation effects could be greater for the interstitial case than for the substitutional case. In all cases, deep defects were found in the energy gap only for cation-site s-like orbitals or anion-site p-like orbitals and, in the substitutional case, only the latter were appreciably affected by relaxation. For substitutional impurities in these materials, x-values (concentration of Cd) ranging from 0.1 to 0.3 were considered. In both the substitutional and interstitial cases, extensive calculations were performed for x-values which corresponded to a band-gap of 0.1eV. In the substitutional case, it was found that I, Se, S, Rn, and N were possible defect candidates for the formation of cation-site s-like levels, while Zn and Mg were candidates for anion-site p-like levels. In the interstitial case, deep defect levels were found in the band-gap for Au, Ag, Hg, Cd, Cu, and Zn for the cation site, and N, Ar, O, and F for the anion site. In the substitutional case, it was possible for relaxation to move the levels into the band-gap whereas, in the interstitial case, it was possible for relaxation to move them out of the band-gap. Perturbation theory was used to study the effect of non-parabolicity upon shallow donor levels, and it was discovered that it could increase binding by some 10%. Although the absolute accuracy of the results was limited, the chemical trends were accurately predicted.

W.Li, J.D.Patterson: Physical Review B, 1994, 50[20], 14903-10