Deep levels due to chalcogen defects in Si–Ge solid solutions

Abstract

The electronic structure of Si_xGe_1−x solid solutions has been calculated using the second-neighbour tight-binding theory in the virtual-crystal approximation. Considering the effects both of changes in the diagonal as well as the nearest-neighbour off-diagonal interaction integrals in the perturbation potential, we have calculated the deep energy levels of the sp-bonded substitutional defects in terms of the well-known κ-space Green function theory. A simple method, incorporating only the Herman-Skillman atomic term values, is also used to estimate the local distortion around the chalcogen (S, Se, Te) impurities in Si and Ge hosts. With the proper choice of relaxation parameter, the impurity levels are found to be in good qualitative agreement with the existing experimental and theoretical data.