Impurity dependence of phonon-assisted tunneling in n-Ge

Phonon-assisted tunneling was investigated in n-Ge metal-semiconductor junctions as a function of impurity concentration in the semiconductor. The contributions to the conductance due to the LA, TA, LO and TO phonons were measured and the relative contribution of LA to TA and LA to TO phonons was found to depend on impurity concentration. This is in disagreement with the theory based on the ‘second order process’ and indicates that other processes should also be considered.