  Germanium single crystal having 45 mm diameter and 100 mm length of 7N+
purity has been grown by Czochralski method. Structural quality of the crystal
has been characterized by Laue diffraction. Electrical conduction and Hall
measurements are carried out on samples retrieved from different parts of the
crystal along the growth axis. Top part of the crystal exhibits lowest impurity
concentration (~10^12/cm3) that gradually increases towards the bottom
(10^13/cm3). The crystal is n-type at room temperature and the resistivity
shows non-monotonic temperature dependence. There is a transition from n-type
to p-type conductivity below room temperature at which bulk resistivity shows
maximum and dip in carrier mobility. This intrinsic to extrinsic transition
regions shift towards room temperature as the impurity concentration increases
and reflects the purity level of the crystal. Similar trend is observed in
boron implanted high purity germanium (HPGe) crystal at different doping level.
The phenomena can be understood as a result of interplay between temperature
dependent conduction mechanism driven by impurity band and intrinsic carrier in
Ge crystals having fairly low acceptor concentrations (<10^12/cm3).
