Abstract: A heterostructure includes a stained epitaxial layer of either silicon or germanium that is located overlying a silicon substrate, with a spatially graded Ge.sub.x Si.sub.1-x epitaxial layer overlain by a ungraded Ge.sub.x.sbsb.0 Si.sub.1-x.sbsb.0 intervening between the silicon substrate and the strained layer. Such a heterostructure can serve as a foundation for such devices as surface emitting LEDs, either n-channel or p-channel silicon-based MODFETs, and either n-channel or p-channel silicon-based MOSFETs.

Abstract: The invention is predicated upon the discovery by applicants that exposure of a Ge surface to arsenic produces a drastic change in the step structure of the Ge surface. Subsequent exposure to Ga and growth of GaAs produces three-dimensional growth and a high threading dislocation density at the GaAs/Ge interface. However exposure of the Ge surface to Ga does not substantially change the Ge step structure, and subsequent growth of GaAs is two-dimensional with little increase in threading dislocation density. Thus a high quality semiconductor heterostructure of gallium arsenide on germanium can be made by exposing a germanium surface in an environment substantially free of arsenic, depositing a layer of gallium on the surface and then growing a layer of gallium arsenide. The improved method can be employed to make a variety of optoelectronic devices such as light-emitting diodes.