In accordance with the bond formation of impurity atoms in semiconductors, a wave function of the local molecular type was admixed into the band function. We obtained an effective mass-equation with an additional term of the S function type. In the case of simple band structure, the influence of atomic character on the ionization energy, and the relation between the shallow and the deep levels were discussed. Further more, we analyzed the valley-orbit splitting caused by the existance of several equivalent minima of conduction band in Ge and Si. Because of the interaction between bonds, the variation of wave function of a shallow level is small, but the correction on the ionization energy may be appreciable. This is in agreement with the hyper-fine structure data of the electron spin resonance.
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