Low-temperature epitaxial crystallization of amorphous Ge_xSi_1-x and NiSi₂ layers on Si induced by ion irradiation

Crystalline Ge_xSi_1-x alloy and NiSi₂ layers grown on Si substrates and amorphized by ion irradiation at -196°C are shown to recrystallize epitaxially during subsequent high-energy ion irradiation at temperatures of 275 and 45° C, respectively. For Ge_xSi_1-x alloys, where the amorphous layer extended into the underlying Si substrate, both commensurate and incommensurate epitaxy were obtained. Furthermore, the dependence of the commensurate/incommensurate transformation on alloy composition was found to be similar to that for layers grown by molecular beam epitaxy. For NiSi₂ layers, ion irradiation at 45° C was found to simultaneously crystallize the amorphous NiSi₂ layer and amorphize the underlying Si substrate. This is shown to result in a novel layered structure consisting of a crystalline NiSi₂ layer which is epitaxially aligned with the (111) Si substrate but separated from it by an amorphous Si layer.