Effect of AlGaN and InAlGaN Barrier Layers on the Performance of GaN-based HEMTs on Sapphire Substrates

This study presents a quantitative comparison of GaN-based high electron mobility transistors (HEMTs) employing InAlGaN and AlGaN barrier layers, focusing on DC, RF, and capacitance characteristics. The InAlGaN-based HEMT achieves a maximum drain current exceeding 2.0 A/mm at VDS = 10 V, whereas the AlGaN-based HEMT device delivers 1.6 A/mm under the same bias. The threshold voltage shifts from approximately –5 V for AlGaN to –6 V for InAlGaN HEMTs. Peak transconductance (gm) improves from 0.2 to 0.3 mS/mm, resulting in an increase in unity current-gain cut-off frequency (fT) from 15 to 18 GHz. Capacitance analysis shows maximum CGD values of 1.8 × 10–12 F/mm (AlGaN-based HEMT) and 2.0 × 10–12 F/mm (InAlGaN-based HEMT), while CGS increases from just below 2.0 × 10–12 to 2.5 × 10–12 F/mm. Both devices exhibit off-state leakage currents below 10–13 A/mm; however, the InAlGaN HEMT supports a superior breakdown voltage of ~870 V, compared to ~700 V for AlGaN HEMT device. These results demonstrate that InAlGaN barriers significantly enhance current drive, RF performance, and breakdown robustness of the HEMT devices.