Separation of thin films from transparent substrates by selective optical processing

DETAILED DESCRIPTION The invention may be summarized as a method of transferring a crystalline film from a growth substrate to an acceptor substrate.
The film of one composition is grown on a substrate of another composition having an absorption edge at a shorter wavelength than that of the grown film.
The film side of the structure is then bonded to an acceptor substrate.
A strong optical beam irradiates the side of the structure having the growth substrate with radiation that passes through the growth substrate but which is strongly absorbed in the film, thereby weakening the interfacial bond due to localized decomposition of the film at the interface.
The intensity of the radiation is, however, low enough to not cause the irradiated area to separate.
Preferably, the laser is raster scanned over an area larger than that of the laser beam.
A separation process is performed after the completion of the laser irradiation.
In the example of a GaN thin film, the separation process may include heating the structure to above the melting point of gallium, which is 30.
degree.
C.
Chemical separation processes may also be used.
Alternatively, a sacrificial layer may be grown between the desired film and the growth substrate.
The optical beam absorbed by the sacrificial layer can then irradiate from the side of either the growth or acceptor substrate that is transparent to the optical beam.
The acceptor substrate may be flexible, for example, an elastomeric substrate.
In this case, the film may be laser scribed along cleavage planes, and then the flexible substrate is bent to cleave the film at desired facets.