Mobility of Holes and Electrons in High Electric Fields

The field dependence of mobility has been determined for electrons and holes in both germanium and silicon. The observed critical field at 298^∘{}K beyond which μ varies as E^-1/2 is 900 volts/cm for n-type germanium, 1400 volts/cm for p-type germanium, 2500 volts/cm for n-type silicon, and 7500 volts/cm for p-type silicon. These values of critical field are between two to four times those calculated on the basis of spherical constant energy surfaces in the Brillouin zone. A saturation drift velocity of 6(10)⁶ cm/sec is observed in germanium which is in good agreement with predictions based on scattering by the optical modes. Data on n-type germanium at 20^∘{}K show a range over which impurity scattering decreases and the mobility increases with field until lattice scattering dominates as at the higher temperatures.