Waveguide integrated graphene–colloidal-quantum-dot photodetectors with high gain and 2.7  MHz bandwidth

The realization of high responsivity, high sensitivity, fast response, and wide operation band photodetection in silicon photonics is currently a critical challenge for emerging applications such as on-chip optical sensing and spectroscopy. In this work, we present a promising solution by integrating a graphene–colloidal-quantum-dot (CQD) heterostructure onto a silicon waveguide platform to construct photodetectors with large photogating gain, without needing complex layered structures. Waveguide integration confines light and CQDs within a compact active region featuring short channel length and absorption length. Leveraging graphene’s low density of states and high mobility, the device simultaneously achieves high-responsivity, high-sensitivity, and high-speed performance. The device achieved a responsivity of 1.1×10 5 AW −1 to 4 AW −1 and a noise equivalent power (NEP) of 1.27×10 −4 to 2.03 pW Hz −0.5 when subjected to input optical power ranging from 56 pW to 3 μW at 1.55 μm. Notably, a substantial bandwidth of 2.7 MHz was reached, outperforming the high-gain counterparts based on the photogating effect. By adjusting the energy band of the graphene–CQD heterostructure, the manipulation of the photogating response is realized, offering valuable insights for further optimization of the high-gain photodetectors. Furthermore, we demonstrate dynamic tuning of the graphene–CQD heterostructure band alignment via an integrated gate electrode, enabling the modulation of the photogating response while elucidating the underlying mechanism. This approach provides a good pathway for performance improvement of similar photogating devices. In the future, this platform can be readily extended to longer wavelengths (e.g., mid-infrared) through straightforward adjustments to CQD synthesis parameters or material composition, complemented by protective-layer passivation for enhanced operational stability. With its compatibility with scalable fabrication processes, this architecture holds significant promise for broadband, high-sensitivity, high-speed, on-chip photodetection applications.