  Fabrication of diode by forming n-type electrical contact on germanium (Ge)
and its AC impedance analysis is important for radiation detection in the form
of pulses. In this work lithium (Li) metal has been electro-deposited on p-type
Ge single crystal from molten lithium nitrate at 260{\deg}C. The depth of Li
diffusion in Ge was successfully varied by changing the electroplating time as
determined by sheet resistance (SR) measurement after successive lapping of Ge
surface. Li is found to diffuse up to 500 micron inside Ge by heat treatment of
as deposited Li/Ge at 350{\deg}C for 1 hour. A stable n-type electrical contact
on Ge with SR ~1 ohm/square and impurity concentration ~3.7x10^15/cm^3 is
developed by Li incorporation in p-type Ge crystal showing net carrier
concentration ~3.4x10^10/cm^3 and SR ~100 Kohm/square. Acceptor concentration
determined from the 1/C^2 vs V plot shows similar temperature dependence as
found by Hall measurement. The fabricated n+/p junction exhibit ideal diode
characteristics with gradual increase in cut off voltage at low temperatures.
Under forward bias, junction capacitance mainly comprises of diffusion
capacitance (~10 micro.F) showing strong frequency dependence and the impedance
is partly resistive resulting in semicircular Cole-Cole plot. Imaginary
impedance spectra reveal that the relaxation time for the diffusion of majority
carriers decreases at higher temperatures and increased forward voltages. The
diode is purely capacitive under reverse bias showing a line parallel to the
y-axis in the Cole-Cole plot with frequency independent (100Hz-100MHz)
depletion capacitance ~10pF.
