Objective Thin-film lithium niobate (TFLN) inherits excellent intrinsic properties of bulk lithium niobate and features high refractive index contrast, strong optical field confinement and device miniaturization capability. It has become a core platform for next-generation photonic integrated circuits. However, the wide bandgap, weak light absorption and low electrical conductivity of TFLN prevent it from achieving efficient photodetection independently. Heterogeneous integration with high photosensitivity materials is the core technical solution to this problem. Transition metal dichalcogenides (TMDs), especially 2H-phase molybdenum ditelluride (2H-MoTe₂), exhibit narrow bandgap, strong near-infrared absorption and good compatibility with TFLN platforms, making them ideal photosensitive materials for TFLN waveguide-integrated photodetectors. Existing TFLN waveguide-integrated two-dimensional material photodetectors mostly rely on external bias voltage to separate and transport photogenerated carriers, which increases system power consumption and circuit design complexity. Existing self-powered detection schemes suffer from poor compatibility with TFLN planar microfabrication processes, and easily introduce interface defects and lattice damage. This work aims to develop a low-power, high-compatibility and high-performance self-powered photodetector integrated on TFLN waveguide platform.

Methods The device was fabricated based on TFLN proton-exchange waveguide platform. Few-layer 2H-MoTe₂ was used as both light absorption layer and carrier transport channel. An asymmetric Schottky junction was constructed using gold (Au) and mechanically exfoliated few-layer graphite (Gr) electrodes with distinct work functions. All contacts between MoTe₂ and electrodes were realized by dry transfer process to form van der Waals heterointerfaces, which avoided Fermi level pinning effect and interface damage caused by traditional metal evaporation. The device structure consisted of a 500 μm thick silicon substrate, a 2 μm thick SiO₂ dielectric cladding layer, and a 0.5 μm thick x-cut lithium niobate single-crystal thin film with 5 μm wide proton-exchange waveguides. The source electrode was a evaporated Au (30 nm)/Cr (40 nm) stack, and the drain electrode was few-layer Gr prepared by dry transfer. Atomic force microscopy (AFM) was used to characterize the thickness of Gr and MoTe₂ layers. Raman spectroscopy was employed to verify the crystal phase and structural integrity of the materials after transfer. An Au/MoTe₂/Au field-effect transistor was fabricated to determine the carrier type of MoTe₂. A photoelectric test system was built to measure the I-V characteristics, photocurrent-power dependence, photoresponse time and dark current noise power spectral density of the device at 1310 nm communication wavelength. The actual optical power coupled into the waveguide was calibrated using a reference waveguide with identical dimensions.

Results and Discussions The Au-MoTe₂-Gr photodetector was successfully fabricated and exhibited both self-powered and bias-driven operation modes. AFM characterization showed that the thickness of Gr layer was approximately 35 nm and that of MoTe₂ layer was about 25 nm. Raman spectra confirmed that both materials maintained excellent 2H crystal phase without phase transition or lattice damage after dry transfer. The transfer characteristic curve of the Au/MoTe₂/Au transistor indicated typical p-type semiconductor transport behavior of the few-layer MoTe₂. Energy band analysis revealed that Au formed a high-barrier Schottky contact with MoTe₂, while Gr formed a low-barrier contact. A net built-in electric field directed from Gr to Au was established in the channel, which drove the separation and transport of photogenerated electron-hole pairs at zero bias voltage. The I-V curves showed obvious unidirectional rectification characteristics in dark environment, verifying the successful construction of the asymmetric Schottky junction. Under 0.5 V forward bias, the device achieved a maximum responsivity of 42.65 mA/W at 1310 nm wavelength. In self-powered mode, the responsivity reaches 2.22 mA/W and the maximum optical on/off ratio is as high as 2.1 × 10⁶. This result is at a relatively high level among reported waveguide-integrated photodetectors, demonstrating its good application potential in on-chip integrated photonic systems. The device exhibited fast photoresponse speed, with rise time of 81 μs and fall time of 291 μs in self-powered mode, corresponding to a bandwidth of approximately 4.3 kHz. The specific detectivity was calculated to be 7.5 × 10⁷ Jones under self-powered operation. The photocurrent showed sublinear dependence on incident optical power, with power-law exponents of 0.47 under 0.5 V bias and 0.55 in self-powered mode. This phenomenon was attributed to the saturation of trap states and enhanced carrier recombination in the MoTe₂ channel with increasing incident optical power.

Conclusions The Au-Gr asymmetric Schottky junction design provides a practical technical path for low-power and high-compatibility self-powered photodetection on TFLN waveguide platforms. The fabricated device achieves stable dual-mode operation at 1310 nm communication wavelength, combining high on/off ratio, fast photoresponse and low power consumption. It demonstrates great application potential in on-chip integrated photonic systems.