I. Introduction
InP-Based High-Electron Mobility Transistors (HEMTs) and heterojunction bipolar transistors (HBTs) have shown great success in microwave and millimeter-wave applications. Both device technologies are excellent choices for operation in the terahertz regime. In fact, for the last 20 years, InP-based transistors have held the record of frequency response as assessed by the current-gain cutoff frequency and the maximum oscillation frequency . Current records for are 765 GHz in pseudomorphic InGaAs/InP HBTs [1] and 610 GHz in pseudomorphic InGaAs/InP HEMTs [2], and those of are 1.2 THz in HEMTs [3] and 800 GHz in HBTs [4]. These remarkable results have been achieved through the combination of downscaling of minimum feature size and parasitics reduction, and the use of active regions with very high electron velocities.