Electrical Compact Modeling of SiGe Phototransistor: Impact of the Distributed Nature on Dynamic Behavior

This article presents and analyzes an improved electrical compact model of SiGe/Si-double heterojunction bipolar phototransistors (HPT). This is a complete one, operating in dc, in nonlinear large-signal ac mode and in optomicrowave operating. This HPT was fabricated based on an existing industrial SiGe heterojunction bipolar transistor (HBT) Telefunken GmbH technology. Several deviations from the standard HBT electrical behavior are observed when the optical access on the top of the HPT was created. A compact, physically based model is then proposed to take into account these phenomena called “2-D electrical extension effect,” which explains the 2-D and distributed nature of charge carriers flow within the SiGe HPT. Parameter extraction, verification, and validation of the dynamic behavior model are done by RF characterization, through S-parameters and transition frequency curves, and by the optomicrowave gain of the optical characteristics over a wide frequency range.