Al 2 O 3 ‐based surface passivation and insulated gate structure for AlGaN/GaN HFETs

A novel Al2O3-based passivation and insulated gate (IG) structure has successfully applied to AlGaN/GaN heterostructure field-effect transistors (HFETs). Al2O3 was formed by a molecular beam deposition of Al followed by its oxidation using the electron-cyclotron-resonance (ECR) excited O2 plasma in an ultrahigh vacuum environment. A large conduction-band offset of 2.1 eV was obtained at the Al2O3/Al0.3Ga0.7N interface, leading to the pronounced reduction of gate leakage currents. The fabricated IG-type HFETs exhibited good gate control of drain currents up to VGS = +3 V. The maximum transconductance was 130 mS/mm. No current collapse was observed in the Al2O3 IG HFETs under the pulse-mode gate stress, indicating remarkable passivation effects of the present Al2O3-based insulated gate and passivation structure. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)