N-doping by P implantation into pre-amorphized Ge and subsequent annealing: P diffusion, solid-phase-epitaxial regrowth and P activation

P and As are considered the most suitable n-dopants in Ge. However, because of diffusion and deactivation effects it is difficult to achieve highly-n-doped Ge by ion implantation and subsequent annealing. We investigated high fluence P implantation into pre-amorphized Ge and subsequent annealing. The thickness of the amorphous layer was varied by implanting Ge at different energies. In all cases the main part of the as-implanted P profiles is located within this layer. Both RTA and flash-lamp annealing were employed. Considering samples with amorphous layers of different thickness enables detailed investigations of P diffusion in amorphous and crystalline Ge and solid-phase epitaxial regrowth during the post-implantation annealing. The thickness of the amorphous layers and the quality of the regrown crystalline Ge were monitored by RBS/C. The chemical depth profiles of P and the donor depth distributions were measured by SIMS and SRP, respectively. The results indicate that P diffuses much faster in amorphous Ge than in crystalline Ge. It is assumed that the P diffusivity in amorphous Ge shows a concentration dependence similar to that in crystalline Ge. The solid-phase epitaxial regrowth occurs already at the lowest thermal budget used in this work. It causes a considerable P redistribution and, presumably, the incorporation of P into crystalline Ge at concentrations above the equilibrium solubility.