Amorphization kinetics of germanium under ion implantation

Amorphization of germanium (Ge) substrates under ion implantation has been studied by transmission electron microscopy. Ge crystalline wafers were implanted with 150 keV Ge ions with doses ranging from 1×1013–1×1016 cm−2. First a distribution of disordered zones appears, and then a continuous amorphous layer forms by damage accumulation and finally reaches the surface. The thickness of this layer increases while the roughness of the crystalline–amorphous interface decreases with further increase in the dose. For doses up to 5×1015 cm−2, Ge behaves like silicon and the amorphization of Ge can be described by using the critical damage energy density model. We show that the kinetics of Ge amorphization can be quantitatively predicted by assuming that amorphization occurs in regions which have received more than 5 eV/atom.Yet for high doses, approximately from 5×1015 cm−2, the Ge surface undergoes a topology change and the well-known cellular structure appears.