Suppression of current collapse in insulated gate AlGaN/GaN heterostructure field-effect transistors using ultrathin Al2O3 dielectric

We investigated effects of electronic states at free surfaces of AlGaN/GaN heterostructure field-effect transistors (HFETs) on the inner current transport at the heterointerfaces. The analysis on transient currents for the air-exposed and H2-plasma-treated devices showed that N-vacancy-related near-surface traps play an important role in current collapse in AlGaN/GaN HFETs. An Al2O3-based surface passivation scheme including an N2-plasma surface treatment was proposed and applied to an insulated-gate HFET. A large conduction-band offset of 2.1 eV was achieved at the Al2O3/Al0.3Ga0.7N interface. No current collapse was observed in the fabricated Al2O3 insulated-gate HFETs under both drain stress and gate stress.