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

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.