On the diffusion and activation of ion-implanted n-type dopants in germanium

Abstract

Some unresolved issues with respect to diffusion and activation of n-type ion-implanted dopants in germanium and of particular interest for shallow junction formation are pointed out and critically discussed. In particular, the absence of extrinsic diffusion during rapid thermal annealing at electron concentrations in the range of a few times 1019 cm−3 and the occurrence of a saturation dopant activation level of the order of 5×1019 cm−3 have been investigated more closely. It is shown that the former can be understood by considering a diffusivity enhancement factor (n/ni)2, with n the free electron concentration and ni the intrinsic carrier concentration, respectively. The saturation of the dopant activation, on the other hand, is determined by the density of states in a degenerately doped semiconductor. Based on these insights, some guidelines for controlling the excess n-type dopant diffusion and activation in germanium can be derived.