Dirac Surface‐State Driven Broad Spectral Band Low Quantum Energy Photoresponse in Quaternary Topological BiSbSe ₂ Te

2D topological materials are garnering significant interest for their potential in optoelectronic applications, particularly due to their unique quantum transport properties and exceptional optical characteristics. In this work, quaternary topological BiSbSe₂Te with stoichiometry modulation from Bi₂Se₃ are synthesized and demonstrates a broad spectral band photoresponse, ranging from infrared to terahertz and to millimeter waves, with a particular excellence on detection of low quantum energy photons. The observed photoresponse is attributed to the excitation of plasmonic nonequilibrium electrons originating from the topological Dirac surface states inherent in the BiSbSe₂Te. The detector exhibits remarkable performance, achieving a responsivity of 8174 V/W and a noise equivalent power of 4.7 × 10^- ¹ ³ W/Hz^1/2 at 0.094 THz, with a wide low quantum energy terahertz and millimeter wave photoresponse spanning from 0.032 to 0.173 THz. The study underscores the potential of Dirac surface-state driven photoresponse in BiSbSe₂Te, paving the way for the development of sensitive, broad spectral band and room-temperature low quantum energy photodetectors, which are highly pursued for a variety of applications.