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First Observation of Bias Oscillations in GaN Gunn Diodes on GaN Substrate

In this paper, we report on the bias oscillation of GaN-based Gunn diodes realized on a n+-GaN substrate. Different contact materials, ambient gases, and pulsewidths were used and compared with regard to device stability. A wide negative- differential-resistance (NDR) region was measured for electrical- field values E larger than a threshold field Eth of 150 kV/cm. Electrical fields much higher than the threshold value did not lead to any electromigration effects or discharging problems from the contacts. The drift velocity derived from the current-voltage characteristics, diode geometry, and doping concentration in the active layer was estimated to be 1.9 times 107 cm/s. Bias oscillations were obtained for the GaN Gunn diodes in the presence of a series inductance.