Low-cost, high-efficiency, and high-speed SiGe phototransistors in commercial BiCMOS

We present a new approach to obtain low-cost and high-performance SiGe phototransistors in a commercial BiCMOS process. Photoresponsivity of 2.7 A/W was obtained for 850-nm detection due to the transistor gain, corresponding to 393% quantum efficiency. Responsivities of 0.13 A/W and 0.07 mA/W were achieved for 1060 and 1310 nm with SiGe absorption. With V-ce = 2 V, we measure a -3-dB bandwidth of up to 5.3 GHz for phototransistors with a 4-mu m(2) active area and 2.0 GHz for phototransistors with 60-mu m(2) active area and finger contacts. This high-efficiency and high-speed phototransistor is an enabling device for monolithic receiver integration.