An excellent cutoff frequency (f(t)) as high as 400 GHz was successfully re
alized in 45-nm-gate pseudomorphic InGaAs/InAlAs high electron mobility tra
nsistors (HEMTs). An additional vertical gate-recess suppressed short-chann
el effects, while keeping good pinchoff characteristics. Gate length (L-g)
dependence of electron transit time (tau (transit)) implied an increased sa
turation velocity (v(s)) of 3.6 x 10(7) cm/s in the developed pseudomorphic
HEMTs. This f(t) is the highest value ever reported for any transistors to
date.