Waveguide-Integrated Two-Dimensional Material Photodetectors in Thin-Film Lithium Niobate

Thin-film lithium niobate on insulator (LNOI) is a promising platform for optical communications, microwave photonics, and quantum technologies. While many high-performance devices like electro-optic modulators and frequency comb sources have been achieved on LNOI platform, it remains challenging to realize photodetectors (PDs) on LNOI platform using simple and low-cost fabrication techniques. 2D materials are excellent candidates to achieve photodetection since they feature strong light-matter interaction, excellent mechanical flexibility, and potential large-scale complementary metal–oxide–semiconductor-compatible fabrication. Herein, this demand is addressed using an LNOI-2D material platform, and two types of high-performance LNOI waveguide-integrated 2D material PDs, namely graphene and tellurium (Te), are addressed. Specifically, the LNOI-graphene PDs feature broadband operations at telecom and visible wavelengths, high normalized photocurrent-to-dark current ratios up to 3 × 10⁶  W⁻¹, and large 3-dB photoelectric bandwidths of ≈40 GHz, simultaneously. The LNOI-Te PDs on the other hand provide ultrahigh responsivities of 7 A  W⁻¹ under 0.5 V bias for telecom signals while supporting GHz frequency responses. The results show that the versatile properties of 2D materials and their excellent compatibility with LNOI waveguides could provide important low-cost solutions for system operating point monitoring and high-speed photoelectric conversion in future LNOI photonic integrated circuits. © 2023 The Authors. Advanced Photonics Research published by Wiley-VCH GmbH