Alloy‐Engineered WS2xSe2(1−x) Photodetector for Broadband Fast and Low‐Noise Response

ABSTRACT Alloy engineering in 2D transition metal dichalcogenides enables precise bandgap and defect‐state modulation for high‐performance photodetection. Here, we systematically investigate two‐terminal photodetectors based on alloys with compositions 0.76, 0.58, and 0.32. Although the spectral response is composition‐dependent, the alloy with exhibits superior optoelectronic performance. This enhancement is attributed to the conversion of deep‐level defects, prevalent in ‐ and ‐rich phases, into shallow defect states in the compositionally balanced ternary alloy. Carriers trapped in shallow states are readily thermally re‐excited into the conduction band, suppressing trap‐assisted recombination and improving carrier transport. The optimized device (8.1 nm thick) demonstrates broadband photoresponse from 300 to 900 nm, peaking near 650 nm, consistent with its direct bandgap. It achieves a maximum responsivity of 1.45 A , detectivity of Jones, noise‐equivalent power of W , and fast response times of 15 µs (rise) and 12 µs (decay), corresponding to a 3 dB bandwidth of 23 kHz. The responsivity increases 3.3‐fold at 403 K, indicating thermally robust operation. These results highlight defect‐engineered alloys as promising candidates for fast, low‐noise, broadband photodetectors.