Optimizing performance to achieve multi-terahertz operating frequencies in pseudomorphic HEMTs

High-electron mobility transistors (HEMTs) are important for high frequency applications, and they now operate in the range of several hundred GHz for the cut-off frequency, f_T and even higher for the maximum frequency of oscillation, f_max. To study the question of how much higher these frequencies can be pushed, we have used a full-band, cellular Monte Carlo transport program to study scaled pseudomorphic HEMTs and their response at high frequency. Building on a previous study on f_T, we have obtained the unilateral power gain for gate lengths ranging from 10 to 50 nm, extracted the corresponding f_max's and extrapolated the results to determine an ultimate frequency limit for the 300 nm long device shown here.. We find that f_max can exceed 4 THz, ~25% higher than the limit for f_T that was previously obtained. We also examine the effect of varying the gate to channel spacing has on the operation of these devices.