Al_2O_3-based surface passivation and insulated gate structure for AlGaN/GaN HFETs

摘要

A novel Al_2O_3-based passivation and insulated gate (IG) structure has successfully applied to AlGaN/GaN heterostructure field-effect transistors (HFETs). Al_2O_3 was formed by a molecular beam deposition of Al followed by its oxidation using the electron-cyclotron-resonance (ECR) excited O_2 plasma in an ultrahigh vacuum environment. A large conduction-band offset of 2.1 eV was obtained at the Al_2O_3/Al_(0.3)Ga_(0.7)N interface, leading to the pronounced reduction of gate leakage currents. The fabricated IG-type HFETs exhibited good gate control of drain currents up to V_(GS) = +3 V. The maximum transconductance was 130 mS/mm. No current collapse was observed in the Al_2O_3 IG HFETs under the pulse-mode gate stress, indicating remarkable passivation effects of the present Al_2O_3-based insulated gate and passivation structure.