ONSET OF CURRENT OSCILLATIONS IN EXTRINSIC SEMICONDUCTORS UNDER DC VOLTAGE BIAS

We present a model which describes the onset of current instabilities and space-charge domains in extrinsic semiconductors (especially p-Ge) under DC voltage bias. Just above the onset voltage for current insta bility we have found numerically small-amplitude fast oscillations due to the periodic motion of solitary waves which decay before reaching the receiving contact. For slightly larger applied voltages there is a n abrupt and slightly hysteretic transition to slower large-amplitude solitary waves similar to those in the Gunn effect. An amplitude equat ion is derived for long samples which reveals a quasicontinuum of osci llatory modes that become linearly unstable at onset.