InP/GaAsSb Double Heterojunction Bipolar Transistor Emitter-Fin Technology With fMAX = 1.2 THz

We report a new InP/GaAsSb double heterojunction bipolar transistor (DHBT) emitter fin architecture with a record {f}_{\mathrm {MAX}} =1.2 THz, a simultaneous {f}_{\mathrm {T}} =475 GHz, and BV_{\mathrm {CEO}} =5.4 V. The resulting BV_{\mathrm {CEO}}\,\times \,{f}_{\mathrm {MAX}} =6.48 THz-V is unparalleled in semiconductor technology. Devices were realized with a 20-nm-thick compositionally and impurity graded GaAsSb-base and a 125-nm InP collector. The performance arises because the process allows: 1) a tunable base-emitter access distance down to 10 nm; 2) the use of thicker base contact metals; and 3) the minimization of parasitic capacitances and resistances via precise lateral wet etching of the base-collector (B/C) mesa. Perhaps more significantly, InP/GaAsSb DHBTs with {f}_{\mathrm {MAX}} \ge1 THz are demonstrated with emitter lengths as long as 9.4 \mu \text{m} and areas as high as 1.645 \mu \text{m} 2 . Such an area is > 6\times larger than previously reported terahertz (THz) DHBTs, representing a breakthrough in THz transistor scalability. This attractive performance level is achieved with a very low dissipated power density which makes InP/GaAsSb DHBTs well-suited for high-efficiency millimeter- and submillimeter-wave applications. Furthermore, we provide the first large-signal characterization of a THz transistor with 94 GHz load-pull measurements showing a peak power-added-efficiency (PAE) of 32.5% (40% collector efficiency) and a maximum saturated power of 6.67 mW/ \mu \text{m} 2 or 1.17 mW/ \mu \text{m} of emitter length in a common-emitter configuration. Devices operate stably under large-signal conditions, with voltages nearly twice higher than those for peak small-signal performance.