Electron Velocity Enhancement in Laterally Scaled GaN DH-HEMTs With $f_{T}$ of 260 GHz

In this letter, we report the first experimental observation of electron velocity enhancement by aggressive lateral scaling of GaN HEMTs. Through reduction of the source-drain distance down to 170 nm using n⁺-GaN ohmic regrowth, 45-nm gate AlN/GaN/Al_0.08Ga_0.92N HEMTs exhibited an extremely small on resistance of 0.44 Ω·mm , a high maximum drain current density of 2.3 A/mm, a high peak extrinsic transconductance of 905 mS/mm, and a record fT/f_max of 260/394 GHz. Delay time analysis showed that the outstanding fT was mainly due to significantly reduced electron transit time at higher drain-source voltages resulting from suppressed drain delay and enhanced electron velocity in the laterally scaled GaN HEMTs.