High performance normally-off Al2O3/GaN MOSFETs with record high threshold voltage by interface charge engineering

An efficient approach to engineering the Al2O3/GaN positive interface fixed charges (Qit+) by post-dielectric annealing in nitrogen is demonstrated. The remarkable reduction of interface fixed charges from 1.44×1013 to 3×1012 cm−2 was observed, which leads to a record high threshold voltage (VTH) of +7.6 V obtained in the Al2O3/GaN MOSFETs. The positive interface charges were proposed originating from the N-vacancy and O-substitution at the Al2O3/GaN interface and validated by Ab initio study. The device with dimensions of LG/LGS/LGD/WG = 2/1.5/5/50 µm delivers a high drain current density of 355 mA/mm. A high breakdown voltage of 1054 V @ 1 µA/mm was measured in the device with LGD of 20 µm. The results reveal that the method reported in this work is promising in pushing the VTH more positive and simultaneously achieving good device performance of normally-off GaN power devices.