Theoretical calculations of mobility enhancement in strained silicon

The conductivity enhancement of n-doped Si due to strain has been calculated by solving the Boltzmann equation within the relaxation-time approximation. For $T=0$, we determined the Fermi surface from first principles, whereas for $T>0$, we modeled the Fermi surface using the effective-mass approximation. We explain the saturation of the conductivity enhancement with increasing strain in terms of the topology of the Fermi surface. We find in accordance with experiment a decreasing enhancement with increasing doping concentration.