Integrated waveguide PIN photodiodes exploiting lateral Si/Ge/Si heterojunction.

Germanium photodetectors are considered to be mature components in the silicon photonics device library. They are critical for applications in sensing, communications, or optical interconnects. In this work, we report on design, fabrication, and experimental demonstration of an integrated waveguide PIN photodiode architecture that calls upon lateral double Silicon/Germanium/Silicon (Si/Ge/Si) heterojunctions. This photodiode configuration takes advantage of the compatibility with contact process steps of silicon modulators, yielding reduced fabrication complexity for transmitters and offering high-performance optical characteristics, viable for high-speed and efficient operation near 1.55 μm wavelengths. More specifically, we experimentally obtained at a reverse voltage of 1V a dark current lower than 10 nA, a responsivity higher than 1.1 A/W, and a 3 dB opto-electrical cut-off frequency over 50 GHz. The combined benefits of decreased process complexity and high-performance device operation pave the way towards attractive integration strategies to deploy cost-effective photonic transceivers on silicon-on-insulator substrates.