and thus the conductivity mobility and the Hall mobility are equal. Although the high field limit simplifies use of the Hall mobility considerably, excessively high magnetic fields can cause problems due to the quantization of the hole orbits in a magnetic field [I]. The quantization of the particle motion in a magnetic field will create Landau levels within the band. The Landau levels will modify the density of states in the valence band which could affect the interpretation of experimental,data [56]. Another high magnetic field effect of importance is the "magnetic freeze out" which occurs with the stronger localization of bound state wave-functions in a strong magnetic field [62]. Due to the more localized charge distribution, the Coulomb binding energy of the impurity state is increased so that at a fixed temperature the concentration of thermally excited charge carriers will be smaller and the Hall coefficient will be effectively increased.

     Thus, in order to avoid these high field region complications and obtain an experimental determination of the value of conductivity mobility in the low field limit, it is necessary to have an accurate knowledge of the Hall factor with which to modify measured Hall mobilities. Hall measurements are routinely used to experimentally determine the density of ionized impurities in a semiconductor sample. This determination is possible only if an accurate value of the Hall factor for the particular temperature and dopant density considered is available.


 5.2 The Hall Factor

      The Hall and conductivity mobilities are related by the Hall factor as follows: