Ultracompact on-chip coiled waveguide-integrated photodetectors enabled by 2D materials with enhanced responsivity

High-performance on-chip photodetectors are critical for next-generation integrated photonic systems that enable efficient sensing, optical communication, and light detection. Waveguide-integrated two-dimensional (2D) materials, among various material platforms, offer promising solutions for enhanced light-matter interactions due to their remarkable electrical and optical properties. In this article, we have simulated and experimentally demonstrated, for the first time, an ultracompact MoS₂-based photodetector integrated with a coiled silicon nitride waveguide, which is designed to maximize the light-matter interaction by increasing the optical light absorption and improving the responsivity and external quantum efficiency. In contrast to the conventional straight waveguide integration with 2D materials, the coiled waveguide architecture with the MoS₂ flake significantly extends the optical interaction length, which allows prolonged evanescent interaction with the MoS₂ flake, resulting in an increase in responsivity of over 500% compared to a referenced straight waveguide structure. Our fabricated coiled structural photodetector achieves an excellent responsivity of 600 mAW^-1, an external quantum efficiency of 145%, a normalized photocurrent-to-dark current ratio of 9.35 × 10¹⁴ AW^-3, and a noise equivalent power of 1.72 × 10^-9 W under optimal operating conditions. The coiled waveguide's performance confirms that this architecture maximizes optical absorption and photocurrent by extending the light-matter interaction length.