  The impact of neutral impurity scattering of electrons on the charge drift
mobility in high purity n-type germanium crystals at 77 Kelvin is investigated.
We calculated the contributions from ionized impurity scattering, lattice
scattering, and neutral impurity scattering to the total charge drift mobility
using theoretical models. The experimental data such as charge carrier
concentration, mobility and resistivity are measured by Hall Effect system at
77 Kelvin. The neutral impurity concentration is derived from the Matthiessen's
rule using the measured Hall mobility and ionized impurity concentration. The
radial distribution of the neutral impurity concentration in the self-grown
crystals is determined. Consequently, we demonstrated that neutral impurity
scattering is a significant contribution to the charge drift mobility, which
has a dependence on the concentration of neutral impurities in high purity
n-type germanium crystal.
