Lithium niobate waveguide-integrated BiTe/graphene heterojunction photodetector.

We demonstrate an on-chip photodetector by integrating a graphene and topological insulator BiTe heterostructure on a thin-film lithium niobate waveguide. Lithium niobate on insulator (LNOI) waveguides are fabricated by the photolithography-assisted chemical mechanical etching method. The bismuth telluride (BiTe) and graphene heterostructure design provides enhanced photocurrent due to the effective photocarrier generation. The lithium niobate waveguide-integrated BiTe/graphene heterojunction presents a high absorption coefficient of 2.1 dB/µm. The BiTe/graphene heterojunction photodetector exhibits a responsivity of 2.54 mA/W without external bias at a 1.55 µm wavelength, which is enhancement of sevenfold as compared to the pure graphene-based photodetector. The photodetector has a 3 dB bandwidth of over 4.7 GHz. This work provides a potentially viable method for a self-powered, high responsivity, and fast response of the photodetector integrated with the LNOI photonic platform.