Low-Capacitance Ultrathin InGaAs Membrane Photodetector on Si Slot Waveguide Toward Receiverless System

Optical interconnects are promising approaches for future short-distance communications because electrical interconnects show severe limitations in terms of bandwidth and energy consumption. To replace electrical interconnects with optical interconnects at short distances, reducing the overall energy of optical interconnects is indispensable. As an energy-efficient optical receiver system, a “receiverless” system has been proposed, in which power-consuming electrical amplifiers can be eliminated. However, a photodetector (PD) with low capacitance and high responsivity is required. In this article, we propose a silicon (Si) hybrid PD with an ultrathin InGaAs membrane based on a slot waveguide, which enables low capacitance while maintaining high responsivity. In the proposed structure, the ultrathin InGaAs membrane can eliminate an InP taper; therefore, the fabrication process can be simple, and the strong light confinement in a slot waveguide can reduce the PD length, which results in a lower capacitance. On the basis of simulations and experiments, we successfully demonstrated a PD with a sufficiently low capacitance of 1.9 fF and high responsivity of 1.0 A/W, which paves the way for future optical interconnects at short distances.