Small signal equivalent circuit of illuminated HPTs

This paper describes the behavior of equivalent-circuit parameters of illuminated Heterojunction Photo Transistors (HPTs). The equivalent circuit is based on the Gummel-Poon model. It is clarified that S-parameters and each parameter change in value when the HPT is illuminated. Further, the measured characteristics of illuminated HPTs are compared with the calculated from the proposed model of illuminated HPTs.