Characteristics of Al/Ge Schottky and ohmic contacts at low temperatures

Abstract Schottky barrier contact has been fabricated by thermal deposition of Al on (100) p-Ge (impurity concentration1010/cm3 at 80K) that shows n-type conductivity above 180K due to thermally generated carriers. Both p and n-type Ge exhibits ideal Schottky behavior 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 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.