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 instability 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 an abrupt and slightly hysteretic transition to slower large-amplitude solitary waves similar to those in the Gunn effect. An amplitude equation is derived for long samples which reveals a quasicontinuum of oscillatory modes that become linearly unstable at onset.