Effects of physical parameters of graded AlGaN buffer on DC characteristic and short-channel effects in AlInN/GaN high-electron mobility transistors

Abstract

In GaN high-electron mobility transistors (HEMTs), the graded AlGaN buffer can induce negative polarization charges over the buffer by designing the change direction of Al-content. By simulation, the effects of the physical parameters of the graded buffer [bottom Al-content (xbot) and buffer thickness (tbuf)] on the direct-current characteristics and short-channel effects (SCEs) of Al0.83In0.17N/GaN HEMTs are investigated. The results show that when tbuf is fixed, as xbot increases, threshold voltage, peak of transconductance, drain-induce barrier lower and sub-threshold swing will be approximately saturated. As tbuf decreases, the xbot becomes smaller when the saturation occurs. In the graded buffer design, the recommended xbot range is 0.15–0.2 when tbuf = 0.8–1.2 μm. Moreover, suppressing SCEs can reduce tbuf and increase xbot, but at the cost of a significant lower maximum of drain current. A tradeoff is needed in the choice of tbuf and xbot. Compared to conventional AlGaN buffer, the graded buffer can keep AlInN barrier nominally strain-free in the Al0.83In0.17N/GaN HEMTs.