Sub-bandgap polysilicon photodetector in zero-change CMOS process for telecommunication wavelength.

We report a defect state based guided-wave photoconductive detector at 1360-1630 nm telecommunication wavelength directly in standard microelectronics CMOS processes, with zero in-foundry process modification. The defect states in the polysilicon used to define a transistor gate assists light absorption. The body crystalline silicon helps form an inverse ridge waveguide to confine optical mode. The measured responsivity and dark current at 25 V forward bias are 0.34 A/W and 1.4 μA, respectively. The 3 dB bandwidth of the device is 1 GHz.