Generalized band anti-crossing model for highly mismatched semiconductors applied to BeSe_(x)Te_(1 - x)

We report a new model for highly mismatched semiconductor (HMS) alloys. Based on the Anderson impurity Hamiltonian, the model generalizes the recent band anti-crossing (BAC) model, which successfully explains the band bowing in highly mismatched semiconductors. Our model is formulated in empirical tight-binding (ETB) theory and uses the so called sp$^{3}$s* parameterization. It does not need extra parameters other than bulk ones. The model has been applied to BeSe$_{x}$Te$_{1 - x}$ alloy. BeTe and BeSe are wide-band gap and highly mismatched semiconductors. Calculations show large band bowing, larger on the Se rich side than on the Te rich side. Linear interpolation is used for an arbitrary concentration $x$. The results are applied to calculation of electronic and optical properties of BeSe$_{0.41}$Te$_{0.59}$ lattice matched to Si in a superlattice configuration.