Controllable growth and photodetectors of centimeter-scale 2D ReS2xSe2(1-x) alloy films

Band-gap engineering in two-dimensional (2D) transition metal dichalcogenides (TMDs) is crucial for advancing nanoelectronics and optoelectronic applications. Alloying TMDs with different band gaps enable precise bandgap tuning through compositional control. In this work, centimeter-scale 2D ReS_2xSe_2(1-x) alloy films with a tunable sulfur content (x) were successfully grown on mica substrates via chemical vapor deposition (CVD) by varying the S/Se precursor ratio. The ReS_2xSe_2(1-x) alloy films are polycrystalline films with grain sizes of several nanometers to several tens of nanometers. The back-gated field-effect transistors (FETs) fabricated from these alloys exhibited composition-dependent electrical properties: pure ReS₂ exhibited n-type conduction behavior, whereas pure ReSe₂ and ReS_2xSe_2(1-x) alloys exhibited p-type conduction behavior, with ReS_0.98Se_1.02 achieving the highest hole mobility of 2.6 cm²/(V·s). An ohmic contact was formed between the Au electrodes and alloy channels. Photodetectors based on these alloys displayed composition-tunable spectral responses from the ultraviolet–visible range to the near-infrared range. The alloys with a S content of 2x < 1 exhibited optimal photoresponsivity at 532 nm and 635 nm, whereas those with S composition of 2x > 1 showed superior performance at 405 nm. Photodetectors based on ReS_1.82Se_0.18 have a photoresponsivity of 0.06 AW^-1 and rise/decay times of 0.30/0.10 s under 405 nm light irradiation, respectively, whereas the ReS_0.98Se_1.02-based device has photoresponsivities of 0.02 and 0.02 AW^-1 and rise/decay times of 0.16/0.16 and 0.14/0.12 s under 532 and 635 nm light irradiation, respectively. This trend directly correlates with the composition-tunable bandgap of the alloys. This work advances the scalable synthesis of ReS_2xSe_2(1-x) films and demonstrates their potential for wavelength-selective optoelectronic applications.