N-polar GaN/InAlN/AlGaN MIS-HEMTs with 1.89 S/mm extrinsic transconductance, 4 A/mm drain current, 204 GHz fT and 405 GHz fmax

This paper reports 1.89 S/mm extrinsic transconductance, 4 A/mm drain current density, and 0.23 Ω-mm on-resistance on depletion-mode nitrogen-polar GaN MIS-HEMTs with a 5.4-nm GaN channel and a novel InAlN/AlGaN back barrier grown by MOCVD on a vicinal sapphire substrate. These dc figures of merit are among the best values reported for all GaN HEMTs. Additionally, an f
_T
of 204 GHz using a 70-nm T-gate (14.3 GHz*μm f
_T*
L
_g
product) and an f
_max
of 405 GHz using a 90-nm T-gate were obtained. These frequency figures of merit match the state-of-the-art Ga-polar devices with similar gate lengths. GaN-based HEMTs have demonstrated tremendous performance in high-frequency, high-power applications due to the high electron velocity, sheet charge density, and critical electric field of the III-N material system. The dc and high-frequency performance of N-polar and Ga-polar HEMTs has increased rapidly as the result of highly scaled device dimensions and advanced epitaxial structures [1]-[4].