Abstract
Higher photo-responsivity brings the advantage of reducing device area cost for photodetectors. This work demonstrates that the responsivity of a bipolar phototransistor can be greatly enhanced by reusing the parasitic photo-generated carriers in the substrate. The reuse of parasitic photo-carriers can be realized by strapping the base terminal and the local substrate terminal of a bipolar phototransistor via simple metallic interconnect. Test devices were implemented with a commercially available bipolar-CMOS (BiCMOS) process. Compared with the conventional bipolar phototransistor without reusing the substrate carriers, the proposed phototransistor showed at least one order of magnitude improvement in responsivity. The peak of spectral response shifted from the visible light range into the near-IR region, which is beneficial to near-IR detection.