Bandgap-Tailored (Bi_xSb_1-x)₂Se₃ Thin Films Enabling Fast Broadband Near-Infrared Photodetection and Imaging

Antimony selenide (Sb₂Se₃), a narrow-bandgap semiconductor with strong light absorption, exhibits photoresponse up to ≈1050 nm due to its intrinsic 1.15 eV bandgap. To extend detection into the near-infrared (NIR, 700-1350 nm), Bi-alloyed (Bi_xSb_1-x)₂Se₃ is developed via vacuum sputtering and postselenization. Bi incorporation redshifts the absorption edge to 1350 nm, thereby broadening the photodetection window. At its peak external quantum efficiency of 905 nm, the (Bi_0.21Sb_0.79)₂Se₃ device achieves a responsivity of 1.01 A W^-1 and detectivity of 9.77 × 10¹² Jones, surpassing the undoped counterpart, which shows 0.17 A W^-1 and 8.87 × 10¹² Jones. Importantly, at 1310 nm, the (Bi_0.21Sb_0.79)₂Se₃ device maintains a detectable photocurrent with a responsivity of 0.27 µA W^-1 and detectivity of 4.63 × 10⁷ Jones, confirming the extended spectral response. Under 1064 nm pulsed excitation, it exhibits rise and decay times of 10 and 63 ns, respectively-nearly tenfold faster than the undoped version. These improvements result from Bi-induced bandgap modulation, which optimizes band alignment, suppresses interfacial trap states, and promotes anisotropic carrier transport along the quasi-one-dimensional ribbon structure. This work demonstrates a scalable and low-toxicity approach for achieving extended and fast NIR detection, well-suited for future multispectral imaging and biomedical sensing.