Design of InP Segmented-collector DHBTs with Reduced Collector Transit Time τ c for Large Power Bandwidth Power Amplifiers

InP double-heterojunction bipolar transistors (DHBTs) have demonstrated power gain cutoff frequencies $(f_{max})$ above 1THz under low collector voltage due to electron velocity overshoot in the InP drift collector [1] [2]. Under higher collector voltage, however, a quick onset of $\Gamma-\mathrm{L}$ scattering limits the average electron velocity to the saturation velocity (Fig. 1(a)-(c)), leading to a Johnson's figure-of-merit (JFOM) second to GaN HEMTs and a limited transistor power bandwidth for InP DHBTs [3]. Here we propose a velocity-engineered device structure called the segmented-collector DHBT (SC-DHBT) that incorporates p-type scattering layers within the drift collector to reduce the electron kinetic energy and force a greater electron distribution into the low effective mass $\Gamma-$ valley for extended velocity overshoot (Fig. 3(a)). Transport simulations show the collector transit time $\tau_{c}$ is reduced from 1.23ps in the reference design to 0.90ps in a double scatterer design at $V_{cb}=5\mathrm{V}, J_{c}{=}$ 1mA/um 2 . The proposed SC-DHBT design is suited for large power bandwidth power amplifiers.