Process for forming semiconductor alloys having a desired bandgap

Abstract

An epitaxial layer of a narrow-gap semiconductor is deposited on a substrate comprising a wider-gap semiconductor. The opposite surface of the substrate is then illuminated with light pulses at a wavelength corresponding to the desired bandgap of the resulting material. Each pulse causes localized heating where it first encounters a material having a sufficiently narrow bandgap to be an absorber at the wavelength of illumination. This localized heating will then cause interdiffusion, producing a layer of semiconductor alloy having a bandgap intermediate between the bandgaps of the two starting materials. Repetition of this step will have the effect of moving the region of localized absorption away from the original location, and toward the film/air interface. Since the desired end product composition will be transparent to the illumination applied, the process is inherently self-limiting. By appropriately selecting the wavelength of illumination applied, variously proportioned semiconductor compositions may be obtained, so that the bandgap of the resulting material may be arbitrarily selected to have any desired value between the bandgaps of the two starting materials. No surface damage is caused by this technique.