Experiments and simulation of the diffusion and activation of the n-type dopants P, As, and Sb implanted into germanium

The effects of implant dose and annealing conditions on the diffusion, activation, and out-diffusion of the typical n-type dopants in germanium (phosphorus, arsenic, antimony) were studied. First, short annealing times were used to limit the diffusion of dopants and to match the conditions needed for the realization of shallow junctions. Sb is not well suited to achieve high activation levels because honeycomb voids can already form at doses of 3 × 1014 cm−2. Of the other two, P is a better candidate than As because it was possible to maximize the activation level to up to about 4.5 × 1019 cm−3 without noticeable diffusion. This absolute value has only a limited accuracy, though, since the mobility models available in literature lead to values which differ by more than one order of magnitude. Longer annealing times were then used to study the redistribution of the dopants. For P, a model based on migration predominantly via complexes with doubly negatively charged vacancies and dopant loss was implemented which allowed the simultaneous simulation of our experimental profiles with one set of parameters. The extracted diffusion coefficient with an activation energy of 2.2 eV is comparable to the results obtained in previous studies. No noticeable P clustering was observed in these experiments. The model was then adapted to simulate the redistribution of As and Sb. For Sb, clustering is apparent in the diffusion profiles and has to be taken into account in the simulations.