Analytical Model for the Threshold Voltage of ${p}$ -(Al)GaN High-Electron-Mobility Transistors

An analytical model for the calculation of the threshold voltage for enhancement-mode (E-mode) ${p}$ -(Al)GaN high-electron-mobility transistors (HEMTs) is presented. The ON-state behavior (at low output voltages) of both ${p}$ -GaN HEMTs and ${p}$ -AlGaN HEMTs—including the gate injection transistor—are discussed in detail, and closed expressions for the threshold voltage ${V}_{T}$ of both devices are deduced. It is found that the threshold voltage values for both devices are close to one another, and that there is an ideal upper limit when the ${p}$ -type doping in the AlGaN gate is perfectly tailored, yielding more positive threshold voltages. This ideal case might be difficult to realize technologically, but can serve as a benchmark for the ${V}_{T}$ of ${p}$ -(Al)GaN HEMTs.