Simulation study on electrical properties of p-GaN gate normally-off HEMT devices affected by Al mole fraction in AlGaN barrier layer

Abstract

The reason that p-GaN gate normally-off high electron mobility transistor (HEMT) device is able to draw prevail interests is not only for its outstanding electric properties of low on-resistance and high thermal conductivity, but also for its applications under high frequency and high voltage. In HEMT devices, the setting of Al component in the AlGaN barrier layer is a key parameter to affect the formation of two-dimensional electron gas (2DEG) at the AlGaN/GaN heterojunction, and therefore directly determines the performance of the devices. This paper uses the Atlas module of the Silvaco-TCAD software to design and simulate p-GaN gate normally-off HEMT devices to investigate the effect of Al mole fraction content in the AlGaN barrier layer on the electrical performance, as well as the causes in terms of the conduction band energy structure diagram. The results show that the threshold voltage of the HEMT device decreases, the maximum saturation drain current increases, and the peak transductance of the HEMT device increases with increasing the Al content. In the off-state (zero gate voltage), the AlGaN/GaN potential well depth becomes deeper as the Al mole fraction increases, resulting in a lower driven force to rebuild the minimized 2DEG concentration in the GaN layer for switching from off-state to on-state, and this leads to a lower threshold voltage. While, in the on-state (5 V gate voltage), the deeper AlGaN/GaN potential well depth as the Al mole fraction increases, the higher of the 2DEG concentration of the GaN layer, leading to a higher maximum saturation output drain current. After optimization, the integrated electrical performance of the HEMT devices has been found best when the Al mole fraction content is about 0.25. The results obtained from the simulations are helpful for the experimental design of p-GaN gate normally-off HEMT devices