Broadband sub-bandgap linear photodetection in Ge+-implanted silicon waveguide photodiode monitors

The power monitor, a crucial component for programmable photonics, faces challenges in on-chip applications due to rigorous demands for low optical absorption loss, adequate responsivity, minimal dark current, and low power consumption. Currently, there are limited effective solutions that can simultaneously address all these issues within the existing photodetection technology for telecommunications bands on the silicon-on-insulator platform. Here, we present a first Ge+-implanted silicon waveguide photodiode (PD) monitor operating in the dual-band spanning telecommunications O- and C-bands. Ge, a complementary metal-oxide-semiconductor-compatible group IV element, can substitute a silicon atom at a lattice site with minimal introduction of extra free carriers. We demonstrate responsivities of 124.8 mA·W−1·mm−1 at 1310-nm wavelength (O-band) and of 31.2 mA·W−1·mm−1 at 1550-nm wavelength (C-band), with a low dark current of 0.8 nA upon a small bias voltage of −3 V. The internal quantum efficiency exceeds that of B+-, P−-, and Ar+-implanted silicon PDs by factors of 4.9 to 16.8. The device exhibits optical absorption loss of <0.012 dB·μm−1 and 98% linearity across <1 mW on-chip power. Our Ge+-implanted silicon waveguide PDs hold significant promise in on-chip power monitors for programmable photonics.