Tight-binding Green’s-function approach to off-center defects: Nitrogen and oxygen in silicon

We describe a new tight-binding Green's-function approach to defects in semiconductors which is expected to be particularly appropriate for off-center and aggregate systems. The universal two-center-integral expressions used in the tight-binding parametrization provide the mechanism for producing the appropriate Green's-function input for any impurity position. The method is tested here for off-center substitutional nitrogen and oxygen in silicon where we produce single-particle electronic structures and localizations. We discuss these computational results, strengths, and shortcomings of the method, and potential improvements.