Experimental observation of RF avalanche gain in GaN-based PN junction diodes

Radio-frequency (RF) reflection gain in GaN homojunction p-n diode structures has been observed experimentally. A vertical p⁺/n structure grown on a native GaN substrate was used to achieve the high internal electric fields necessary to induce impact ionisation in GaN while minimising the effects of dislocations on the device performance. Amplitude and phase signatures in the measured RF reflection coefficient indicate the onset of impact ionisation within the device, with reflection gain observed at frequencies above 350 MHz. The magnitude of the measured gain is consistent with theoretical estimates of impact ionisation parameters, and the bias dependence of the measured reflection phase response is consistent with avalanche as the gain mechanism.