High phosphorous doped germanium: Dopant diffusion and modeling

The in situ n-type doping of Ge thin films epitaxial grown on Si substrates is limited to 1 x 10(19) cm(-3) by the phosphorous out-diffusion during growth at 600 degrees 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 x 10(19) cm(-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 x 10(19) cm(-3). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4745020]