MEXTRAM modeling of Si-SiGe HPTs

The integration of the photodetector is essential for optical communication chips. The heterojunction phototransistor (HPT) is integrable with the SiGe HBT process and can be modeled by a modified MEXTRAM model for the circuit simulation. The impact ionization to obtain an extra gain for the optoelectronic conversion and the "early voltage reduction" under constant illumination are well modeled in a modified model. The base recombination current (nkT current) and the substrate contact to enhance the HPT speed are incorporated in ac model. It shows a good agreement between measurement and simulation.