Graphene‐like two‐dimensional materials (graphene, transition‐metal dichalcogenides (TMDCs)) have received extraordinary attention owing to their rich physics and potential applications in building nanoelectronic and nanophotonic devices. Recent works have concentrated on increasing the responsivity and extending the operation range to longer wavelengths. However, the weak absorption of gapless graphene, and the large bandgap (>1 eV) and low mobility in TMDCs have limited their spectral usage to only a narrow range in the visible spectrum. In this work, we demonstrate for the first time a high‐performance, antenna‐integrated, black phosphorus (BP)‐based photoconductor with ultra‐broadband detection from the infrared to terahertz frequencies. The good trade‐off between the moderate bandgap and good mobility results in a broad spectral absorption that is superior to that of graphene. Different photoconductive mechanisms, such as photothermoelectric (PTE), bolometric, and electron–hole generation can be distinguished depending on the device geometry, incident wavelength, and power. Especially, the photoconductive response remains highly efficient, even when the photon energy is extended to the terahertz (THz) band at room temperature, which is driven by the thermoelectric‐induced well. The proposed photodetectors have a superior performance with an excellent sensitivity of over 300 V W−1, low noise equivalent power (NEP) (smaller than 1 nW Hz−0.5 (10 pW Hz−0.5) with respect to the incident (absorbed) power), and fast response, all of which play key roles in multispectral biological imaging, remote sensing, and optical communications.

Despite their huge application capabilities, millimeter-and terahertzwave photodetectors still face challenges in the detection scheme. Topological insulators (TIs) are predicted to be promising candidates for long-wavelength photodetection, due to the presence of Dirac fermions in their topologically protected surface states. However, photodetection based on TIs is usually hindered by the large dark current, originating from the mixing of bulk states with topological surface states (TSSs) in most realistic samples of TIs. Here millimeter and terahertz detectors based on a subwavelength metal-TI-metal (MTM) heterostructure are demonstrated. The achieved photoresponse stems from the asymmetric scattering of TSS, driven by the localized surface plasmon-induced terahertz field, which ultimately produces direct photocarriers beyond the interband limit. The device enables high responsivity in both the self-powered and bias modes even at room temperature. The achieved responsivity is over 75 A/W, with response time shorter than 60 ms in the self-powered mode. Remarkably, the responsivity increases by several orders of magnitude in the biased configuration, with the noise-equivalent power (NEP) of 3.6 × 10 −13 W Hz −1/2 and a detectivity of 2.17 × 10 11 cm Hz −1/2 W −1 at room temperature. The detection performances open a way toward realistic exploitation of TIs for large-area, real-time imaging within long-wavelength optoelectronics.