High-performance waveguide photodetectors based on lateral Si/Ge/Si heterojunction

On-chip light detection is universally regarded as a key functionality that enables myriad of applications, including optical communications, sensing, health monitoring or object recognition, to name a few. Silicon is widely used in the micro-electronics industry. However, its electronics bandgap precludes the fabrication of high-performance photodetectors that operate at wavelengths longer that 1.1 μm, a spectral range harnessed by optical communication windows of low fiber attenuation and dispersion. Conversely, Germanium, a group-IV semiconductor as Silicon, with a cut-off wavelength of ~1.8 μm, yields efficient light detection at near-infrared wavelengths. Germanium-based photodetectors are mature building blocks in the library of silicon nanophotonic devices, with a low dark-current, a fast response, a high responsivity and low power consumption with an established fabrication flow. In this work, we report on the design, fabrication and operation of waveguide pin photodetectors that advantageously exploit lateral Silicon/Germanium/Silicon heterojunctions. Devices were fabricated on 200 mm silicon-on-insulator substrates using standard micro-electronics production tools and processes. This photodetector architecture takes advantage of the compatibility with contact process steps of silicon modulators, thereby offering substantially reduced fabrication complexity for transmitters and receivers, while providing improved optical characteristics. More specifically, at a lowbias reverse voltage of -1 V, we experimentally achieved dark-currents lower that 10 nA, a device photo-responsivity up to 1.1 A/W, and large 3-dB opto-electrical bandwidths over 50 GHz. In addition, high-speed data rate transmission measurements via eye diagram inspection have been conducted, with pin photodetector operation at the conventional 10 Gbps up to the future 40 Gbps link speeds.