A direct calculation of the tunnelling current. III. Effect of localized impurity states in the barrier

Abstract

For Pt. II see ibid., vol.4, 2598 (1971). The effect of an impurity level located in the barrier of a metal-insulator-metal tunnelling junction is investigated with the help of a new formalism. In agreement with Hurault's results (1971) it is found that a sharp resonance peak appears in the d2I/dV2 characteristic, when the impurity state energy crosses either electrode Fermi level. The width of this resonance peak is proportional to the width of the virtual bound state arising from the interaction of the two electrode continuum with the impurity state. It is stressed that the resonance effect cannot be interpreted as the opening of a new tunnelling channel. The dependence of the effect on the location of the impurity state is briefly studied.