Photodetection with Gate-Controlled Lateral BJTs from Standard CMOS Technology

The silicon-based gate-controlled lateral bipolar junction transistor (BJT) is a controllable four-terminal photodetector with very high responsivity at low-light intensities. It is a hybrid device composed of a MOSFET, a lateral BJT, and a vertical BJT. Using sufficient gate bias to operate the MOS transistor in inversion mode, the photodetector allows for increasing the photocurrent gain by $10^{6}$ at low light intensities when the base-emitter voltage is smaller than 0.4 V, and BJT is off. Two operation modes, with constant voltage bias between gate and emitter/source terminals and between gate and base/body terminals, allow for tuning the photoresponse from sublinear to slightly above linear, satisfying the application requirements for wide dynamic range, high-contrast, or linear imaging. MOSFETs from a standard 0.18-$\mu{\rm m}$ triple-well complementary-metal oxide semiconductor technology with a width to length ratio of 8 $\mu{\rm m}$/2 $\mu{\rm m}$ and a total area of ${\sim}{\rm 500} \mu{\rm m}^{2}$ are used. When using this area, the responsivities are 16–20 kA/W.