High f _T and f _max AlGaN/GaN HFETs achieved by using thin and high-Al-composition AlGaN barrier layers and Cat-CVD SiN passivation

We fabricated sub-0.1 μm-gate Al_0.4Ga_0.6N/GaN heterostructure field-effect transistors (HFETs) with AlGaN barrier thicknesses of 4–10 nm. The devices were passivated with 2 nm-thick SiN layers formed by catalytic chemical vapor deposition (Cat-CVD). The Cat-CVD SiN passivation greatly increased electron density, and the effect became more significant with decreasing AlGaN barrier thickness. The HFETs had maximum drain current densities of 1.1–1.5 A/mm and peak extrinsic transconductances of 305–438 mS/mm. Peak current-gain cutoff frequency of 163 GHz and maximum oscillation frequency of 192 GHz were obtained for the devices with 8 nm-thick AlGaN barriers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)