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Enhancement-mode (E-mode) GaN-based MIS-HEMTs still suffer from undeniable gate leakage or low gate breakdown voltage due to the low quality of gate dielectrics, resulting in a notorious tailing effect of the off-state current. In this letter, a gate scheme featuring SiON/Al2O3 stack dielectrics and partially recessed gate barrier has been employed in the AlGaN/GaN MIS-HEMTs. A high on/off current ratio over $10^{{9}}$ and a small threshold voltage ( ${V} _{\text {th}}$ ) hysteresis less than 20 mV are achieved in the fabricated E-mode devices with a ${V} _{\text {th}}$ around 2.5 V, mainly owing to the reduction of the net positive fixed charge density in the SiON/Al2O3 gate stack confirmed by the ${C}$ - ${V}$ measurements. Meanwhile, a good performance uniformity on 6-inch wafer is achieved which demonstrates the promising scheme for fabricating GaN-based E-mode MIS-HEMT products.

Buffer related electron trapping and hot electron injection are responsible for R on degradation in devices, but the effects of substrate termination are still uncertain. In this work, both positive and negative substrate bias are applied to investigate the different vertical trapping mechanisms in 650 V gallium nitride (GaN) power devices. R on shows an instant and significant increase under vertical bias stress, and the magnitude of downward buffer electron trapping induced R on increase is relatively larger than that induced by upward trapping. Additionally, the substrate floated and grounded GaN devices are also submitted to both off-state and semi-on-state stresses to investigate the effects of substrate termination on hot electron injection induced R on increase. The intensity of the upward electron trapping increases faster with temperature resulting in a higher R on increase than the downward situation. The hot electron effect is only obvious when the substrate is grounded, suggesting that the main injection destination is not in the buffer. The substrate floated device exhibits a lower R on increase after both off-state and semi-on-state stresses at elevated temperatures. Substrate floated packages are suggested to ensure reliable dynamic performance of device, especially for high voltage application design.