  We have calculated electronic and optical properties of
Si/BeSe$_{0.41}$Te$_{0.59}$ heterostructures by a semiempirical $sp^{3}s^{*}$
tight-binding method. Tight-binding parameters and band bowing of
BeSe$_{0.41}$Te$_{0.59}$ are considered through a recent model for highly
mismatched semiconductor alloys. The band bowing and the measurements of
conduction band offset lead to a type II heterostucture for
Si/BeSe$_{0.41}$Te$_{0.59}$ with conduction band minimum in the Si layer and
valence band maximum in the BeSe$_{0.41}$Te$_{0.59}$ layer. The electronic
structure and optical properties of various (Si$_{2})_{n
}$/(BeSe$_{0.41}$Te$_{0.59})_{m}$ [001] superlattices have been considered. Two
bands of interface states were found within the bandgap of bulk Si. Our
calculations indicate that the optical edges are below the fundamental bandgap
of bulk Si and the transitions are optically allowed.
