A Plasma Instability Induced by Electron-Hole Generation in Impact Ionization

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Abstract
Existence of a new kind of plasma density instability, caused by the dependence of the plasma generation rate on the electric field, is predicted, and lower frequency oscillations believed due to it have been observed experimentally. The observed oscillations, induced by shunting the plasma with an external capacitance, are damped and of frequency 2∼10 Mc/sec in n‐InSb at 77°K. The electron‐hole generation rate has been calculated from the observations and is found to vary approximately as the eighth power of the electric field, with values from about 106 to 108 sec−1 for electric fields between 2.3 and 4.0×104 V/m. When a small external transverse magnetic field was applied, the generation rate increased, but obeyed the identical relationship as a function of electric field as observed in zero magnetic field. Evaluation of the threshold conditions for instability indicates that the microwave radiation observed from an impact‐ionization plasma in InSb can be the result of this density instability.

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