Experimental Evidence of Sustainable Avalanche Operation in E-mode GaN HEMTs

Sustainable avalanche operation was demonstrated and investigated on lateral E-mode GaN HEMT devices with sub-micrometer gate length. Through an extensive analysis: a) we demonstrated that sustainable avalanche operation is made possible by the presence of a subthreshold drain-source leakage, that initiates impact ionization; b) this process clamps the drain voltage to values lower than the dielectric breakdown voltage, thus preventing the catastrophic failure of the devices; c) avalanche operation is sustainable, and the related voltage strongly depends on the device geometry; d) spectrally resolved electroluminescence measurements demonstrate the presence of band-to-band luminescence, ascribed to recombination of holes, generated by impact ionization during the process. Finally, e) the positive temperature coefficient of avalanche voltage has been demonstrated. Support to the interpretation was obtained based on TCAD simulations.