Method of producing buried porous silicon-geramanium layers in monocrystalline silicon lattices

DETAILED DESCRIPTION The ability to synthesize Si based materials with new optical, photonic and electronic properties is greatly desired.
Unfortunately, despite considerable effort, Si based superlattices and quantum wells demonstrated in the art have exhibited limited new properties.
In this invention novel superlattices comprising alternating layers of monocrystalline Si and porous Si--Ge have been fabricated.
This invention is directed towards a lattice having monocrystalline Si layers with embedded porous Si--Ge layers.
The Si layer can be on a Si substrate or wafer.
The product of this invention can have a single layer or multiple layer of porous Si--Ge.
This invention also includes a method for producing such products.
The method is carried out by growing epitaxially Si and Si--Ge layers, followed by patterning or contouring to fabricate a structure which will facilitate wet-chemical solution penetration into the Si--Ge layers.
MBE was used for layer growth, however, other epitaxial techniques will work also.
The patterning of the epitaxially grown layers was carried out in one embodiment of this invention by photolithography and plasma etch in CF.
sub.
4 ; however, other patterning techniques will also work.
In one embodiment the patterning was carried out by argon milling to form mesa structures.
After patterning mesa structures on the epitaxially formed layers, the layers are stain etched with an etchant.
The stain etching is conducted under conditions operable for forming a high density of small pores in the Si--Ge layers with no more than a minor amount of porosification of the Si layers.
By minor amount of porosification of the Si layers as used herein is meant a non-deleterious amount of porosification which allows for some pores at the perimeter or interface with the Si--Ge layers or surface of the Si layers, but no overall porosity throughout the Si layers.
For example we have found that using stain etching under the conditions of this invention, the penetration of the Si--Ge layers is at least about 100 times that of the Si layers which enables total porosification of the SiGe alloy layers and no more than a non-detrimental amount of porosification of the Si layers