Lithium niobate waveguide-integrated Bi₂Te₃/graphene heterojunction photodetector

We demonstrate an on-chip photodetector by integrating graphene and topological insulator Bi₂Te₃ heterostructure on thin film lithium niobate waveguide. The lithium niobite on insulator (LNOI) waveguides are fabricated by photolithography-assisted chemical mechanical etching method. The Bi₂Te₃ and graphene heterostructure design provides enhanced photocurrent due to the effective photocarriers generation. The lithium niobite waveguide-integrated Bi₂Te₃/graphene heterojunction presents a high absorption coefficient of 2.4 dB/μm. The Bi₂Te₃/graphene heterojunction photodetector exhibits a responsivity of 2.5 mA/W without external bias at 1.55 μm wavelength, which is enhancement of 7-fold 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 into the LNOI photonic platform.