InP-based high electron mobility transistors with a very short gate-channel distance

We fabricated 25-nm-gate lattice-matched InAlAs/InGaAs high electron mobility transistors (HEMTs) with a very short gate-channel distance. Using the two-step-recessed gate technique, we reduced the gate-channel distance to 4 nm; We found that the cutoff frequency f(T) increases with decreasing gate-channel distance d. This phenomenon can be explained by an increase in electron velocity under the gate with decreasing d. We obtained an f(T) of 500 GHz with a d of 4 nm. We also fabricated 25-nm-gate pseudomorphic In0.52Al0.48As/In0.7Ga0.3As HEMTs using the same processing technique, and obtained an f(T) of 562 GHz with a d of 4 nm. This f(T) is the highest value yet reported for a transistor of any type.