Processes of p-GaN Gate HEMTs for High-efficiency and High-reliability Applications

This paper reviews the recent progress of p-n junction HEMTs (PNJ-HEMTs) and p-FET bridge HEMTs (PFB-HEMTs). Both device architectures are designed for reliable operation of conventional Schottky-type p-GaN gate HEMTs. PNJ-HEMTs are expected to increase the gate breakdown voltage, thereby avoiding gate breakdown caused by gate voltage oscillations in high-frequency operation. The donor concentration (ND) of n-GaN in PNJ-HEMT is critical for the electric field (E-field) distribution. It was found that a lower ND can widen the depletion region of the p-n junction, thereby reducing the E-field and increasing the maximum gate operating voltage (VGS,max). However, when ND is so low that the n-GaN is completely depleted, the E-field at the vulnerable surface reduces VGS,max. On the other hand, PFB-HEMTs are expected to increase the threshold voltage (VTH) to avoid false turn-on without degrading third-quadrant performance. The on-resistance (Ron) of the p-FET in the PFB-HEMT should be low enough to prevent false turn-on during high-frequency switching applications.