AlGaN/GaN heterostructure field-effect transistors on 4H-SiC substrates with current-gain cutoff frequency of 190GHz

We report on state-of-the-art AlGaN/GaN heterostructure field-effect transistor (HFET) technology in the scope of millimeter-wave applications. 60-nm-long-gate HFETs having 4- and 6-nm-thick Al0.4Ga0.6N barrier layers and SiN passivation layers formed by catalytic chemical vapor deposition (Cat-CVD) were fabricated on 4H-SiC substrates. Both structures had low sheet resistances of 200-220 Omega/sq that were due to not only high mobilities of 1900 - 2000 cm(2)/(V.s) but also high electron densities of (1.4 - 1.7) x 10(13) cm (- 2), which were provided by the high-Al-composition barrier layers and the Cat-CVD SiN. The devices with the 4- and 6-nm-thick barriers had maximum drain current densities of 1.4 and 1.6 A/mm and peak extrinsic transconductances of 448 and 424 mS/mm, respectively. Maximum f(T) and f(max) reached 190 and 251 GHz, respectively. (c) 2008 The Japan Society of Applied Physics.