Silicon (Si) photonic circuits are now widely used for optical interconnects and are being actively developed for many communications, instrumentation, and scientific applications. Active photonic circuit components that, like Si, are made of IV semiconductors—in particular, germanium (Ge)—are easier to integrate than are other semiconductors such as III-V semiconductors (gallium arsenide and so on). As a result, Ge photodetectors, and in particular Ge waveguide coupling detectors, are the subject of much research to improve their bandwidth and saturation power. Researchers from Huazhong University of Science and Technology and Wuhan Research Institute of Posts Telecommunications (both in Wuhan, China) have now demonstrated a Ge photodetector that achieves a bandwidth of greater than 35 GHz and a maximum current density of 1.152 mA/μm3.
The polarization-insensitive device is based on a lumped structure containing two parallel and two related Ge absorption regions sharing the same signal and ground electrodes, which halves the total junction resistance, allowing the absorption region to be doubled to achieve higher power while maintaining bandwidth. A four-port 2D grating guides light into both sides of the Ge regions to use them to the fullest. The bandwidth of 35.84 GHz was measured under a 3 V bias voltage and 0.42 mA photocurrent—the responsivity of the device was 1.06 A/W under these conditions. Reference: G. Chen et al., Opt. Express (May 2, 2016); doi:10.1364/oe.24.010030.
