The Gunn effect under imperfect cathode boundary conditions

Abstract

The usual assumption in the theory of the Gunn effect of a well-behaved cathode is replaced by a more general set of boundary conditions adapted to the treatment of cathode contacts with some interface resistance. The treatment is in terms of a characteristic: that is, the current-field characteristic of the cathode interface itself. For contacts with an interface resistance, the control characteristic lies at least partially below the bulk current-field characteristic. This leads to the primary nucleation of depletion rather than accumulation layers. Depending on the detailed shape of the control characteristic and the location of its crossover point (if any) with the bulk characteristic, a large variety of device behavior can be explained. Examples are Gunn's preoscillation cathode fall, Kennedy's prethreshold amplification behavior, the occurrence of excessive threshold fields for the onset of oscillations, and oscillations with lower amplitude and higher frequency than for well-behaved transit time oscillations, despite good doping homogeneity.