Theory of deep electronic levels of large chalcogen (S, Se, and Te) complexes in Si

Calculations of the deep band-gap electronic states due to large substitutional complexes of the chalcogen impurities S, Se, and Te are described. The complexes considered are those consisting of neighboring impurities of up to five-atom clusters. It is found that the number of gap levels for a given charge state of the cluster is equal to the number of impurities in the complex. In addition, it is found that the electronically active level for a complex of three or more impurities is quite different in wave-function character from that of the isolated impurity, but rather similar to that of a nearest-neighbor pair. The theory predicts a continuous change from deep-level character to nearly-shallow effective-mass-like character as the size of the complex increases. In addition, the theory predicts that several new intracenter transitions between localized bound states are possible. Results are compared with recent experimental observations involving identified and unidentified chalcogen complexes.