Diffusion of phosphorus implanted in germanium

Diffusion experiments of phosphorus introduced by ion implantation in high purity germanium, bare or covered by silicon nitride have been performed at temperatures between 500 °C and 720 °C for times up to 4 h. The distribution profiles of phosphorous have been determined by secondary ion mass spectroscopy. High thermal budget samples show a box-shaped profile and a brutal change in diffusion coefficient, indicating an enhanced diffusion at high concentration of phosphorus. The diffusion coefficient was estimated to 1.2 × 10−18 cm2 s−1 at 523 °C using the double charged vacancies model. However, the poor agreement of computer simulations with the experimental curves indicates that this model is not fully suitable to describe phosphorus diffusion in germanium.Bare samples present a large phosphorus evaporation on annealing (up to 60% of the implanted dose for the highest thermal budget). Si3N4 encapsulation reduces this value to 40% for 4 h annealing at 700 °C (20% for 4 h annealing at 523 °C).