Biasing impact on illuminated SiGe heterojunction phototransistor static performances

A new low-cost BiCMOS Heterojunction Bipolar Phototransistor (HPT) is fabricated for the first time in an industrial BiCMOS technology from STMicroelectronics with a "no change in process" approach. The static responsivity as a function of the biasing is determined from measurements at 850 nm for various HPT designs. Devices with a static responsivity level up to 40 A/W at 2.5V collector-emitter voltage biasing can be achieved when the device operates near its breakdown voltage. In its active region, at VCE = 1V, a static responsivity level up to 12.2 A/W was obtained selecting the appropriate base biasing.