Full-Range Investigation of Drain-Dependent Bidirectional Dynamic Threshold Voltage Shift in Schottky-Type p-GaN Gate HEMT

In this study, the drain-dependent dynamic ${V}_{\text {th}}$ in Schottky-type p-GaN gate HEMT is investigated using a trapezoid-wave-based extraction method, revealing the combined influences of drain stress ( ${V}_{\text {DS-off}}$ ), gate stress ( ${V}_{\text {GS-on}}$ ), and the drain bias, at which ${V}_{\text {th}}$ is measured ( ${V}_{\text {DS-M}}$ ). In the first part of study, the effect of gate stress is minimized by using ${V}_{\text {GS-off}}$ / ${V}_{\text {GS-on}} =0$ V/+3 V. With ${V}_{\text {DS-off}}$ / ${V}_{\text {DS-M}} =390$ /380 V, the device exhibits a severe gate/drain coupled barrier lowering (GDCBL) effect, as is manifested by a negative ${V}_{\text {th}}$ shift of −0.65 V. With ${V}_{\text {DS-off}}$ / ${V}_{\text {DS-M}} =390$ /1 V, the devices suffer from a negative charge storage in the floating p-GaN layer, as manifested by a positive ${V}_{\text {th}}$ shift of +0.87 V. In the second part, the effect of gate stress is included by using ${V}_{\text {GS-off}}$ / ${V}_{\text {GS-on}}= -3$ V/+6 V, which is expected to add to the negative charge storage effect. With ${V}_{\text {DS-off}}$ / ${V}_{\text {DS-M}} =390$ /380 V, the device exhibits a smaller negative ${V}_{\text {th}}$ shift of −0.23 V. With ${V}_{\text {DS-off}}$ / ${V}_{\text {DS-M}} =390$ /1 V, the device exhibits a larger positive ${V}_{\text {th}}$ shift of −1.35 V. The result indicates that the dynamic ${V}_{\text {th}}$ of the device varies bidirectionally with ${V}_{\text {DS}}$ in a switching process, and the shift is highly influenced by the operation condition of the device [i.e., whether the device is operated as a standard power switch (SW) or a field-effect rectifier].