Development of Ultrahigh-Speed InP/GaAsSb/InP DHBTs: Are Terahertz Bandwidth Transistors Realistic?

In response to the continually increasing appetite for bandwidth, most transistor technologies have recently made great strides towards higher cutoff frequencies: Silicon MOSFETs, SiGe HBTs, InP-based HEMTs and a variety of InP -based HBTs all show cutoff frequencies fT and/or fMAX exceeding 300 GHz, and in some cases approaching 800 GHz. Proponents of various technologies have stated that the development of THz bandwidth devices is an attainable milestone for their technology of choice. Such ambitious goals naturally raise the question of whether such performances are in fact realistic given the well-known trends relating breakdown voltages and cutoff frequencies. Can the contending technologies be scaled in a way enabling THz cutoff frequencies while maintaining the well-behaved characteristics of less aggressively scaled previous generations? The present Invited Paper focuses on our efforts to push InP/GaAsSb DHBTs toward THz bandwidths.