Self-powered asymmetric Schottky photodetector integrated with thin-film lithium niobate waveguide

Thin-film lithium niobate (TFLN) has emerged as a key platform for next-generation photonic integrated chips due to its excellent electro-optic, acousto-optic, and nonlinear optical properties, demonstrating numerous advantages in photonic device research. However, constrained by lithium niobate'sinherently low electrical conductivity and weak light absorption, the direct application of TFLN in on-chip photodetectors faces certain challenges. Heterogeneous integration with two-dimensional materials has become an effective solution. Self-driven photodetectors, which operate without an external power supply, offer advantages such as low power consumption and adaptability to complex environments, making them highly promising for practical applications. In this study, the team led by Bingxi Xiang proposed a waveguide-integrated photodetector with an asymmetric Schottky structure. By leveraging the property that internal stress in MoTe₂ can reduce its bandgap, the photovoltaic effect at one of the Schottky junctions was enhanced, enabling the photodetector to exhibit pronounced self-powered behavior.

The bottom electrode serves as the anode beneath MoTe₂, while the top electrode acts as the cathode above MoTe₂. Under van der Waals forces, the MoTe₂ bends at the edge of the bottom electrode, where the induced internal stress reduces the material's bandgap, thereby enhancing light absorption. Compared to the top electrode, the MoTe₂/gold electrode Schottky junction located at the edge of the bottom electrode generates a stronger photovoltaic effect, resulting in a self-powered phenomenon.

The device exhibits a dark current of only −25 pA at −0.5 V, demonstrating significant rectification characteristics. To investigate the origin of this rectifying properties, the researchers designed two device structures. In Structure 1, both electrodes are positioned on top of the material, whereas in Structure 2, the electrodes are both placed beneath the material. The current-voltage (I-V) curves of the two structures show notable difference. Scanning electron microscopy characterization results reveal a clear contrast in surface roughness between the top and bottom sides of the gold electrodes. The disparity in current between the two structures is primarily attributed to the differing quality of the semiconductor–metal interfacial contacts.