High phosphorous doped germanium: Dopant diffusion and modeling

Abstract

The in situ n-type doping of Ge thin films epitaxial grown on Si substrates is limited to 1 × 10[superscript 19] cm[superscript −3] by the phosphorous out-diffusion during growth at 600 °C. By studying the phosphorous diffusion in Ge with different background doping, we find that the diffusion coefficient is extrinsic and is enhanced 100 times in Ge doped at 1 × 10[superscript 19] cm[superscript −3] compared to intrinsic diffusivity. To achieve higher phosphorous concentration, delta-doped layers are used as a dopant source for phosphorous in-diffusion. We show that the doping level is a result of the competition between in-diffusion and dopant loss. The high diffusivity at high n-type carrier concentration leads to a uniform distribution of phosphorous in Ge with the concentration above 3 × 10[superscript 19] cm[superscript −3].