Enhancement mode AlN/ultrathin AlGaN/GaN HEMTs using selective wet etching

The demonstration of device structure incorporating an ultrathin AlGaN barrier capped with a thin AlN layer in the source-drain access region to maintain high 2DEG charge, with a gate opening formed by selective wet etching of the AlN using heated photoresist is reported. AlN/AlGaN/GaN layer structures are grown on a-plane Al₂O₃ substrates by metalorganic chemical vapour deposition. In conclusion, the process is employed using 4 nm AlGaN barrier to demonstrate HEMTs with a threshold voltage of +0.21 V while maintaining a high mobility (>700 cm²/V-s) and with little loss in current density relative to an unetched device.