Artificial Fine-Tuned van Hove Singularity in Twisted Bilayer and Double-Twist Trilayer Graphene with Enhanced Absorption for Photodetection and Photoemission in the Near-Infrared II Range

Optical responses of twisted bilayer graphene at targeted wavelengths can be amplified by leveraging energy levels of van Hove singularities (VHS) via tuning periods of moiré superlattices. Therefore, precise control of twist angles as well as the moiré superlattices is necessary for fabricating integrated optoelectronic devices such as photodetectors and emitters. Although recent advances in twist angle control help the observation of correlated states in twisted magic-angle graphene structures, the impact of such precise control on enhanced optical absorption is still under investigation. Here, we employ a cut and stack method to construct tBLG with twist angles finely tuned between 4.6° and 6.6°, aligning the VHS near the telecom band with optimized optical absorption. The effective enhanced optical absorption and interlayer interaction uniformity are confirmed through Raman and reflection contrast spectroscopy. Additionally, we demonstrate increased photodetection responsivity and broadband upconversion photothermal emission, both enhanced by VHS, under resonant laser excitation. The study further explores a double-twist trilayer graphene configuration, resulting in better enhanced absorption due to the generation of additional VHS points. Our results underscore the potential of precisely engineered twisted structures in advancing the performance of optoelectronic devices.