Avalanche Plasma Production and Instabilities on Subnanosecond Time Scales. II

Abstract

The rapid changes in current occurring during impact ionization are measured as a function of field strength and time in bulk single crystals of n - and p -type InSb at 77°K. A sampling technique is used to record these events on subnanosecond time scales. Several parameters of impact ionization are directly obtained including durations of avalanche (which are dependent on applied voltage amplitude), electric field strengths at the onset of breakdown, peak electric field developed during avalanche, and current rise-rates. During the production of plasma by avalanching in either n - or p -InSb, an event requiring 1.5 to 4.5 nsec, instabilities are observed as oscillations in the field strength. Since they persist only during avalanche, observing these oscillations requires subnanosecond detecting systems. Another type of instability, so far observed only in n -InSb, displays itself as a discontinuous decrease in field strength of ∼200 V/cm during avalanche and of gradually lessening magnitude during the following ∼200 nsec. The lower field portion of these I-E characteristics exhibits oscillations. The establishment of an impact-ionized plasma in equilibrium requires 200 to 300 nsec.