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 $\mu$ varies as $E^{-\frac{1}{2}}$ 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 ${6\left(10\right)\mathrm{}}^6$ 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.

• Received 2 February 1953

DOI:https://doi.org/10.1103/PhysRev.90.766