GaAs avalanche microwave oscillators

Oscillations in the microwave region have been obtained from reverse biased GaAs diodes. Both diffused junctions and surface barrier structures have been employed with breakdown voltages ranging roughly from 20 to 70 volts. Typically, the current densities associated with the oscillating condition are in the range 10³to 10⁴amperes/cm²All observations have been made at room temperature on a pulse basis (one percent to twenty percent duty cycle) with the exception of two units which were operated CW. The oscillations are thought to be of the avalanche transit-time type, with the drift space being the space-charge region itself. On this basis, for the device geometries employed to date, the fundamental frequencies of oscillation are expected to lie primarily between 30 and 100 GHz, somewhat beyond the range conveniently accessible to the detection equipment employed. The observed oscillations have been mainly in the region of 8 to 30 GHz and are thought to be, for the most part, parametric lower sidebands, excited by the (unobserved) fundamental. A pulse output of 40 mW at 27 GHz has been measured, corresponding to an efficiency of 2 percent.