Analysis of Electrical Characteristics of InAlGaN/GaN-Based High Electron Mobility Transistors with AlGaN Back Barriers

In this study, the effect of an AlGaN back-barrier on the electrical characteristics of InAlGaN/GaN high electron mobility transistors (HEMTs) was investigated. The dependence of the thickness and the Al composition of the AlGaN back-barrier on the off-state current (I_off) of the devices was investigated. An InAlGaN/GaN HEMT with an Al_0.1GaN back-barrier of thickness 20 nm exhibited lower I _off because of the carrier confinement effect, which was caused by the back-barrier. The carrier confinement effect also improved the maximum output current density and the transconductance (g _m). Thus, the obtained cut-off frequency (f _T) and maximum oscillation frequency (f _max) values for the InAlGaN/GaN HEMT with the 20 nm thick AlGaN back-barrier were 2.6% and 13% higher than those without the AlGaN back-barrier. In addition, the impact of the buffer trap density and GaN channel thickness were evaluated. In the case of a thickness of 20 nm for the Al_0.1GaN back-barrier, a low I _off was maintained although the trap density in the buffer layer was changed. In addition, as the gate length (L _Ga) decreased to 50 nm, the InAlGaN/GaN HEMT with the 20 nm thick Al_0.1GaN back-barrier achieved better I _off characteristics, lower drain-induced barrier lowering (DIBL) of 85.8 mV/V, and subthreshold swing (S) of 269 mV/dec owing to a reduction in the short-channel effect.