FINE-STRUCTURE IN THE ENERGY-DEPENDENCE OF CURRENT-DENSITY AND OSCILLATIONS IN THE CURRENT-VOLTAGE CHARACTERISTICS OF TUNNEL-JUNCTIONS

We present a theoretical model for the current oscillations observed in tunnel heterojunction diodes. The model is based on the assumption that the only scattering mechanisms operating in the active region of the diode are due to the electron interaction with optical phonons and charged impurities. This allows us to introduce a new transport characteristic, the reduced differential current, whose divergence vanishes. This property (similar to that of the total current) gives a constructive way of determining the mobility in a quasineutral region of the sample, whose modulation by the applied voltage leads to the observed current oscillations. We argue that the current in the quasineutral region is space-charge-limited and can be calculated within the virtual-cathode approximation. Existence of a virtual cathode is due to a large thermodiffusive component of the current at the boundary between the depletion and quasineutral regions, where electrons lose most of their kinetic energy over a short distance. The calculated current oscillations are in good quantitative agreement with experiment. © 1990 The American Physical Society.