Physical understanding of a normally off p-GaN/AlGaN/GaN HEMT gate stack and a review of VTH measurement techniques

Abstract

In this report, a comprehensive review of the variations in threshold voltage (VTH) that could arise due to different VTH measurement techniques, VTH measurement bias conditions and VTH extraction techniques is made. Notably, a standard deviation of 15% is observed in threshold voltage values due to variations in measurement methodology and bias conditions. This variation is attributed to the change in the dynamic gate charge conditions across the gate stack and lateral electric field conditions across the gate and drain, which occur due to the change in measurement conditions and the bias conditions, respectively. No significant variations arise due to the VTH extraction technique. Additionally, a simplified physical interpretation of the gate stack in normally off p-GaN gate/AlGaN/GaN on Si high electron mobility transistors is made. The formation of the two-dimensional electron gas, the charge balance within the p-GaN/AlGaN/GaN gate stack and an analytical expression for the threshold voltage are reviewed and examined. Furthermore, various trapping mechanisms within the gate stack are reviewed to comprehend the dynamic conditions potentially contributing to threshold voltage instability during nominal operation.