Normally-off AlGaN/GaN HEMTs with InGaN cap layer: A theoretical study

AlGaN/GaN high electron mobility transistors (HEMTs) are favored for the use in high-power and high-frequency applications. However, in order to successfully apply them in circuit design normally-off HEMTs are needed. Conventional normally-off HEMTs are plagued by several production and performance issues. Recently, a new approach was proposed by Mizutani et al.: a thin InGaN cap layer introduces a polarization field, which raises the conduction band of the AlGaN/GaN interface. As a result a threshold voltage shift to the positive direction is observed. Relying on the experimental work of Mizutani et al. we conduct a theoretical study of the proposed devices. We calibrate our simulation tool against the measured DC characteristics. Using this setup, we can further explore the device specific effects and conduct a predictive analysis of the AC characteristics. The presented methodology is a valuable tool for the design and optimization of novel devices.