Hole mobility and diffusion coefficient in strained and relaxed doped Ge_xSi_1-x alloys

We have calculated the hole mobility and diffusion coefficient in relaxed and strained GexSi1-x alloys grown on 001 Si, taking into account the detailed valence band structure. The acoustic phonon, non-polar optical phonon, alloy as well as ionized impurity scattering are included. Results are reported for Ge fractions varying from 0 to 100 percent, for lattice temperatures between 100 K and 500 K, and the doping concentration varies between 10¹³–10²⁰ cm^-3. Adopted valence band structures rely on the k p perturbation theory and include heavy, light and spin split-off bands. The calculations show that the light hole contribution to the total mobility can be dominant even if the corresponding band population is small. This is due to the small effective mass of the light hole. Calculations also show that the strained mobility components are significantly larger than the relaxed mobility components. The diffusion coefficient has a behavior similar to the total hole mobility.