The charged states of deep defects in these narrow-gap semiconductors were studied. Predictions were made of the deep-defect energy levels, and of the formation energies, of the defects. The effect of relaxation was included for each charged state, and substitutional and interstitial anions and cations as well as vacancies were considered. Greens function techniques were used, and the Haldane-Anderson model was applied to the effects of various charged states. By using a pseudopotential, the ideal vacancy model was generalized so as to be able to consider relaxation. It was noted that chemical trends could be predicted with considerably more accuracy than could the absolute locations of energy levels. The formation energies, which involved differences, could be predicted with an accuracy that was similar to that which was possible in the case of chemical trends. It was found that, the more negatively charged the impurity. the higher was the energy; except that the vacancy energy did not depend strongly upon the charge. The typical charge-state energy shifts of defect levels were about twice those caused by relaxation effects. The formation energies for defects in the same material, and at the same site, were quite similar. On the other hand, the formation energies of various charged states could vary considerably. When attention was restricted to native defects, it was noted that self-interstitials had the lowest formation energy while, for antisites and vacancies, the results were similar.

W.Li, J.D.Patterson: Physical Review B, 1996, 53[23], 15622-30