Waveguide-integrated PdSe/MoS van der Waals heterojunction photodetector on a thin-film lithium niobate platform.

Lithium niobate (LN) photonic devices have been extensively explored due to their distinct material properties. However, the intrinsic wide bandgap and low electrical conductivity of LN prevent its direct application as a photodetection material at telecommunication wavelengths. In this work, a van der Waals heterostructure photodiode composed of a p-type palladium diselenide () layer and an n-type molybdenum disulfide () layer is successfully demonstrated for photodetection at communication wavelengths on a lithium niobate on insulator (LNOI) platform. The LN waveguide-integrated / photodetector exhibits an ultralow dark current of 0.5 nA, a high on/off current ratio of 180, and a responsivity of 0.77 mA/W at zero bias, highlighting its potential for self-powered photodetection. At -1 bias, the device maintains a dark current of only 23 nA while achieving a responsivity of 1.09 mA/W. An excellent linear photoresponse is observed over a wide power range (0.06-92.24 µW) under both zero- and reverse-bias conditions. These results demonstrate the potential of monolithically integrated LNOI photodetectors for high-performance optical communication and on-chip biochemical sensing applications.