Ultrasensitive and High‐Speed Room‐Temperature Sub‐Terahertz Photothermoelectric Detectors: Antenna‐Graphene Hybrid Plasmon and Microcavity Effects

Efficient coupling of terahertz (THz) radiation into the deep‐subwavelength scale and high absorption efficiency are two critical factors for THz detectors. Here, we demonstrate an efficient coupling mechanism mediated by antenna‐graphene hybrid surface plasmon polaritons (HSPPs). The HSPPs enable strong deep‐subwavelength localization and enhancement of the THz electric field. The strongly confined HSPP near field enhances THz energy absorption in graphene, promoting hot‐carrier generation and the resulting photothermoelectric (PTE) response. To suppress the radiative loss of HSPPs, a microcavity was employed to further enhance THz absorption. We demonstrate a sub‐THz PTE detector integrated with the HSPP‐microcavity structure. Under room‐temperature and zero‐bias conditions, the device achieves a high peak responsivity of 619.7 V/W, a low noise equivalent power (NEP) of 10.3 pW/Hz 1/2 and a fast response time of 4.9 ns at the resonant frequency of 89 GHz. Across a broad frequency range of 60–140 GHz, the average NEP of the detector is 26.5 pW/Hz 1/2 . This work demonstrates that the HSPP‐microcavity is an efficient coupling structure for THz optoelectronics.