Normally-Off Metal-Insulator-Semiconductor P-GaN gated AlGaN/GaN high electron mobility transistors with low gate leakage current

•A novel normally-off MIS-HEMT structure combining by p-GaN/AlGaN/GaN and SiNx insulator layer was fabricated.•Due to the MIS gate structure, devices demonstrate a higher Vth, and the effect of insulator layer on Vth was also investigated.•The gate leakage current is limited a relatively low level. And the breakdown voltages of the gate stacks with different SiNx thicknesses are evaluated.•The electron mobility of the 2DEG channel based on the C-V measurements is calculated which can confirm that the SiNx as gate insulator has few effects on channel mobility by varied thickness. In this study, a normally-off AlGaN/GaN metal–insulator-semiconductor high electron mobility transistors (MIS-HEMTs) with p-GaN layer were processed, which possess a high threshold voltage and a low gate leakage current due to metal–insulator-semiconductor (MIS) gate structure. A SiNx layer as the insulator layer was deposited between p-GaN layer and gate electrode. The dependent of device performance on SiNx thickness was investigated. Moreover, the threshold voltage of normally-off MIS-HEMT was emphatically discussed with different insulator layer thickness. It demonstrates that obviously positive shifting for threshold voltage from 1.5 to 6 V was achieved by increasing the SiNx thickness from 0 to 20 nm, while the channel mobility was comparable for all samples. Besides, the introduction of MIS gate structure is also beneficial for suppressing the gate leakage current and improving the maximum gate voltage swing owing to the high breakdown field of approximately 8.3 MV/cm.