Sustainable breakdown in sub-micrometer E-mode GaN HEMTs: Impact of gate bias and process-driven optimization

We investigate the sustainable breakdown operation of lateral E-mode GaN high-electron mobility transistors. First, the dependence of the sustainable breakdown voltage (Vaval) on gate bias was investigated; a reduction in Vaval was observed at increased gate voltage, and ascribed to the progressively increasing sub-threshold conduction. Evidence for hole trapping under the gate was then obtained, by monitoring the threshold voltage variation during the test, and a dedicated measurement routine was used to prove the recombination of trapped electrons with holes generated by impact ionization. Finally, technological solutions to improve the sustainable breakdown characteristics of the devices are proposed and validated, through the analysis of two different process splits.