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 × 10 13 cm ‐2 and a mobility of 1590 cm 2 /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 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)