Theoretical predictions of electronic and optical properties of short-period Ge-rich Si/Ge superlattices are used to demonstrate that the problem of obtaining direct-gap Si-based structures is best addressed from the point of view of removing the indirectness of Ge with biatomic sheets of Si. The concept of a buffer-induced optical window is proposed.

• Received 21 February 1989

DOI:https://doi.org/10.1103/PhysRevB.40.1966