Warm electron tensor in n-Si from first principles

Ab-initio calculations of low-field charge transport properties such as mobility are now routine. However, few calculations beyond this regime have been reported although considerable experimental data exists for the warm electron tensor in Si. Here, we report a first-principles calculation of the warm electron conductivity tensor of electrons in Si. We find that the observed nonparallelism of current and electric field are accurately reproduced, but the decrease in mobility with electric field is overpredicted by around a factor of three. We show that this discrepancy can be mitigated by inclusion of on-shell one electron-two phonon scattering, suggesting that two-phonon processes play an important role in the high-field properties of n-Si.