In these calculations, the properties are determined for a series of extrinsic carrier concentrations ("doping levels") n and temperatures. The doping level is set by adjusting the Fermi level E F in the electronic-structure calculation, and do not take into account the practicalities or potential impacts of doping to obtain a given n. The electron relaxation times are determined approximately by summing the rates from four scattering mechanisms, viz. acoustic deformation potential (ADP), piezoelectric (PIE), polar optical phonon (POP) and ionised impurity (IMP) scattering. Full details of these calculations are provided in Ref. .