AlGaN/GaN Heterostructure Field-Effect Transistors on 4H-SiC Substrates with Current-Gain Cutoff Frequency of 190 GHz

Abstract

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 Ω/sq that were due to not only high mobilities of 1900–2000 cm2/(V·s) but also high electron densities of (1.4-1.7)×1013 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 fT and fmax reached 190 and 251 GHz, respectively.