Oxygen plasma and post-annealing assisted surface oxidation for high-<i>V</i>th E-mode <i>p</i>-GaN HEMTs

This paper proposes an oxygen plasma-assisted surface oxidation technique and demonstrates that thermal annealing in an oxygen atmosphere can effectively accelerate the formation of GaON, thereby improving the threshold voltage and gate breakdown voltage of p-GaN HEMT. The effects of annealing temperature in an oxygen environment after plasma treatment on Ga-O bond strength and p-GaN surface leakage characteristics are systematically investigated. The evolution of the valence band maximum during oxidation was systematically analyzed. Experimental results reveal that the oxidized GaN exhibits a valence band offset of 1.4 ± 0.8 eV compared to initial GaN, which effectively impedes carrier transport in p-GaN and suppresses leakage currents. By optimizing the oxidation process, a 5-nm-thick gate oxide layer was formed on the p-GaN surface within a short duration. Consequently, the p-GaN HEMT demonstrated significant performance enhancements: the threshold voltage increased from 2.1 to 4.4 V, the gate breakdown voltage improved from 9 to 24.1 V, and the operational gate voltage range expanded from 6 to 12 V. These findings validate the efficacy of the oxygen plasma and post-annealing assisted surface oxidation technique, highlighting its potential for advancing high-performance GaN power devices.