Importance of gate-recess structure to the cutoff frequency of ultra-high-speed InGaAs/InAlAs HEMTs

We have succeeded in developing 30-nm-gate lattice-matched InGaAs/InAlAs HEMTs with an extremely high cutoff frequency f/sub t/ of 472 GHz, the highest value yet reported for any transistor. The superior high-speed characteristics of our HEMT were mainly due to a much reduced lateral gate-recess length while maintaining a small gate-to-channel distance, which enhanced the average electron velocity under the gate. We fabricated asymmetrically recessed-gate HEMTs to separately investigate the effect of source- and drain-side recess lengths on f/sub t/, and clarified that the drain-side recess is more critical to a superior f/sub t/. Monte Carlo simulation results were consistent with the experimental observations.