Sensitive Sub-THz Photodetection in Twisted Graphene with Broad Spectral Response.

The exploitation of photo-induced hot-electron effect in graphene has enabled the advancement of ultrafast photodetectors across the visible to sub-terahertz spectrum. However, the inherent challenges of graphene, including its zero-bandgap, linear dispersion, and atomic-scale thickness, impede the device's photo-electrical conversion efficiency, resulting in a relatively moderate responsivity. Here, monolayer-bilayer graphene into a moiré superlattice is stacked to generate gate-tunable bandgaps and significantly modify the band structure, aiming to enhance the device's performance for sensitive broadband photodetection. The dual-gate twisted monolayer-bilayer graphene (TMBG) transistor exhibits consistent response patterns across the entire spectral range, with the response mechanisms identified as the photothermoelectric effect, observed without a bias voltage, and the bolometric effect, activated by applying bias. At a sub-terahertz frequency of 0.3 THz, the transistor demonstrates exceptional performance at a low temperature of 4.5 K, with an optimized external responsivity of 16.9 A W^-1 and a noise equivalent power of 27 fW/Hz^1/2 and the operational temperature range can be extended up to room temperature. These findings highlight moiré graphene as a promising platform for the development of high-performance ultra-broadband detectors, particularly in the sub-terahertz domain.