Quaternary barriers for improved performance of GaN-based HEMTs

Nearly lattice-matched InAlGaN-barriers for GaN-based high electron mobility transistors (HEMTs) have been grown by molecular beam epitaxy (MBE). Hall measurements reveal a sheet carrier density of 1.9 × 1013 cm-2 and a mobility of 1590 cm2/Vs. HEMTs have been processed from both InAlGaN-barrier and conventional AlGaN-barrier heterostructures. The devices with quaternary barrier show advantages in both DC and RF characteristics including a HEMT with 150 nm gate length, a current density of 2.3 A/mm and a peak transconductance of 675 mS/mm (Lim et al., IEEE Electron Device Lett. 31, 671 (2010) [1]). On the other hand, the transistors with ternary barrier exhibit significantly better pinch-off behaviour and lower gate leakage currents. These issues have been successfully addressed in a second process run by improving the MBE growth of InAlGaN and by adding a GaN cap layer to the HEMT heterostructure.