  Schottky barrier contact has been fabricated by thermal deposition of Al on
(100) Ge (impurity concentration~1010/cm3 at 80K) that shows extrinsic p-type
to intrinsic n-type transition near 180K. Both p and n-type Ge exhibits ideal
Schottky behaviour with low reverse current and near unity ideality factors
obtained from the linear form of temperature dependent current-voltage (I-V)
characteristics. The diode current at various temperatures change its direction
at non-zero applied bias that reflects a shift in position of charge neutrality
level (CNL) from the Fermi level of Ge. With the rise in temperature, Schottky
barrier height (SBH) steadily increases for p-Ge that can be understood on the
basis of observed variation in CNL. Values of SBH determined from the zero bias
Richardson plot agrees well with that estimated from the Schottky-Mott rule for
strongly pinned interface. Activation energies are determined from the
Richardson plot at various forward voltages and found to decrease with applied
bias for n-Ge but reduces to zero for p-Ge that shows work function similar to
Al. Annealing of Al/Ge induces regrowth of p-type Al doped Ge layer that
exhibits gradual reduction of Al concentration towards p-Ge crystal. Al doped
Ge(P+)/Ge (P) junction thus fabricated shows linear current-voltage (I-V)
characteristics in the extrinsic region (below 180K). In the intrinsic region
(above 180K), rectification is observed in the I-V curve due to temperature
dependent change in conductivity of both Al doped Ge layer and Ge crystal.
