Fabrication of amorphous-crystalline superlattices in GeSi-Si and GaAs-AlAs

A study is presented of MeV ion beam amorphization of epitaxial superlattices of GeSi-Si and GaAs-AlAs. In both superlattice systems, we observe preferential damage of one layer type (using transmission electron microscopy and Rutherford backscattering). Selective amorphization of the faster-damaging layers is demonstrated at higher doses, allowing us to form amorphous- crystalline (a-c) superlattices of c-Si/a-GeSi and c-AlAs/a-GaAs. By studying the buildup of damage in the two systems, we deduce differences between the ion beam damage processes in group III-V and IV semiconductors. The most marked distinction is that the AlAs layers inhibit amorphization of the GaAs contiguous with the interface, while Si layers do not appear to affect the amorphization of the adjacent GeSi. This leads us to the tentative conclusion that GaAs amorphization is strongly affected by the local concentration of point defects which may diffuse hundreds of angstroms at ≊80 K and recombine in the AlAs layer.