It was recalled that it was found experimentally that twist-bonding a thin layer of epitaxial material to a thick substrate of the same material had the effect of being compliant with respect to the growth of a hetero-epitaxial layer onto the thin layer. The advantage of the compliant substrate was that the hetero-epitaxial layer was of much higher perfection when compared to its growth on a bulk substrate. This was due mainly to the presence of a very low density of threading dislocations in the hetero-epitaxial deposit. It was noted that there was still much to be explained concerning the mechanism by which the compliant substrate accommodated misfit between itself and the hetero-epitaxial layer. The structure of the interface between the compliant substrate and the thick substrate could be tailored so as to obtain the maximum benefit for the epilayer, and that property was studied here. The importance of a high degree of twist between the compliant substrate and the bulk substrate was that it provided a high density of interfacial dislocations. Closely-spaced dislocations, with overlapping cores, approximated the conditions of a free-standing compliant substrate by providing an easy means for the complaint substrate to accommodate elastically the misfit between itself and the hetero-epitaxial film grown on it. In cases which exhibited strong atomic interaction between the compliant substrate and the bulk substrate, the approximation to a free-standing compliant substrate was not as good and the interface could be reasonably described in terms of a dense array of pure screw dislocations. In this case, accommodation of misfit between the hetero-epitaxial film and the compliant substrate could be accomplished by elastically changing the lattice parameter of the compliant substrate so as to meet that of the hetero-epitaxial film. Elastic deformation of the compliant substrate could cause the dense array of pure screw dislocations to reorient itself and thereby introduce an edge component into the interfacial dislocations which accommodated the misfit that was introduced between the compliant substrate and the bulk substrate. The results showed that exact coincidence angles of twist should be avoided. Good compliant substrates could be obtained by wafer-bonding thin compliant substrates of a crystal which was similar to the hetero-epitaxial film, rather than of a material which was similar to the substrate.

Misfit accommodation by compliant substrates W.A.Jesser, J.H.Van der Merwe, P.M.Stoop: Journal of Applied Physics, 1999, 85[4], 2129-39