Enhanced Light–Tellurium Interaction through Evanescent Wave Coupling for High Speed Mid‐Infrared Photodetection

Abstract Mid‐infrared (MIR) waveguide‐integrated photodetector is essential for various applications in the fields of sensing and optical communications. However, it is challenging to integrate traditional MIR photoactive materials such as HgCdTe or III−V compounds with complementary metal‐oxide‐semiconductor (CMOS)‐compatible silicon platform due to the lattice mismatch. Tellurium (Te), a novel van der Waals (vdW) material with a narrow bandgap, high carrier mobility, and great air stability, is a promising candidate for high‐performance MIR detection. Here, high‐quality Te nanosheets are synthesized using a hydrothermal method and their carrier dynamics are characterized by transient reflection spectrum. The effect of mobility anisotropy on response speed is investigated intuitively by a free space phototransistor. Combining the strong evanescent wave of a waveguide architecture with the synergy effect between the carrier collection path and the highest mobility crystal orientation in Te, an integrated Te photodetector with enhanced light–matter interaction and reduced carrier transit time is achieved. For the first time, the MIR waveguide‐integrated Te photodetector with a responsivity of 2.3 A W⁻¹ and a bandwidth of 4 GHz at 2015 nm is realized, which is the highest speed MIR photodetector based on narrow bandgap vdW materials to date.