Waveguide-integrated MoTe₂/MoS₂ heterojunction photodetector on thin-film lithium niobate with ultrahigh on/off ratio and ultralow dark current

We report a waveguide-integrated photodetector based on a MoTe₂/MoS₂ heterojunction on a thin-film lithium niobate (TFLN) platform. The device exhibits excellent performance under both visible and near-infrared illumination. Under a bias voltage of -1 V, the dark current is as low as ~150 pA, with responsivities of 87.9 mA/W at 635 nm and 26.6 mA/W at 1310 nm, obtained under input optical powers of 3.5 nW and 15.4 nW, respectively. Notably, the photodetector operates effectively even at zero bias, achieving responsivities of 36.3 mA/W at 635 nm and 7.8 mA/W at 1310 nm, along with ultra-high optical on/off ratios of 3.7 × 10⁵ at 635 nm and 1.7 × 10⁵ at 1310 nm. The on/off ratios demonstrated by our photodetector rank among the highest reported for waveguide-integrated photodetectors to date. The spectral response extends up to 1550 nm, demonstrating broadband detection capability.