Concentration Dependence of a Diffusion Coefficient at Phosphorus Diffusion in Germanium

Phosphorus diffusion into germanium is carried out at 600°–750°C by using red phosphorus powder as a diffusion source. Source temperatures are maintained at 240° and 430°C, corresponding to low and high surface concentrations, respectively. At low surface concentration, C s 3 – 7 × 10 18 cm − 3 ( C s ∼ n i , n i ; intrinsic carrier concentration at the diffusion temperature ) , concentration profiles agree well with the erfc curves, showing the behavior of Fick's law. While at high surface concentration, C s 5 – 8 × 10 19 cm − 3 ( C s > n i ) , profiles deviate from the erfc curves. Diffusion coefficients depend both on the local and surface concentrations, representing the same result as that of phosphorus diffusion into silicon.