  Terahertz (THz) response of transistor and integrated circuit yields
important information about device parameters and has been used for
distinguishing between working and defective transistors and circuits. Using a
TCAD model for SiGe HBTs we simulate their current-voltage characteristics and
their response to sub-THz (300\,GHz) radiation. Applying different mixed mode
schemes in TCAD, we simulated the dynamic range of the THz response for SiGe
HBTs and showed that it is comparable with that of the TeraFET detectors. The
HBT response to the variations of the detector design parameters are
investigated at different frequencies with the harmonic balance simulation in
TCAD. These results are useful for the physical design and optimization for the
HBT THz detectors and for the identification of faulty SiGe HBT and Si BiCMOS
circuits using sub-THz or THz scanning.
