A New Current Instability in N-type Germanium

This paper reports the observation of a new oscillatory phenomenon in n-type Ge at 77°K. The effect is a coherent oscillatory component of the current through a bar of n-type Ge with ohmic n+contacts initiated when the average electric field in the sample exceeds some threshold value which is in the region where the electron drift velocity is nearly saturated. The frequencies of the oscillations vary from a few hundred MHz to 2.8 GHz. The effect depends on sample orientation, temperature, and carrier concentration. Some possible mechanisms for this effect are discussed. At somewhat higher fields a second, not necessarily related instability, is also observed.