  The intrinsic performance of "type-II" InP/GaAsSb double heterojunction
bipolar transistors (DHBTs) towards and beyond THz is predicted and analyzed
based on a multi-scale technology computer aided design (TCAD) modeling
platform calibrated against experimental measurements. Two-dimensional
hydrodynamic simulations are combined with 1-D full-band, atomistic quantum
transport calculations to shed light on future DHBT generations whose
dimensions are decreased step-by-step, starting from the current device
configuration. Simulations predict that a peak transit frequency $f_{T,peak}$
of around 1.6 THz could be reached in aggressively scaled type-II DHBTs with a
total thickness of 256 nm and an emitter width $W_E$ of 37.5 nm. The
corresponding breakdown voltage $BV_{CEO}$ is estimated to be 2.2 V. The
investigations are put in perspective with two DHBT performance limiting
factors, self-heating and breakdown characteristics.
