Supersensitive and Broadband Photodetectors Based on High Concentration of Er³⁺/Yb³⁺ Co-doped WS₂ Monolayer

Chemical doping is a significant means to modulate bandgap structures and optoelectronic properties of transition metal dichalcogenides (TMDCs). Herein, an Er3+/Yb3+ co-doped WS2 monolayer with ultrahigh and tunable concentrations is successfully fabricated by in-situ chemical vapor deposition (CVD) technique. The morphologies, thicknesses, components, and structures of the samples are systemically characterized by optical microscope, atomic force microscopy, Raman, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope with energy dispersive spectrometer, and high-resolution transmission electron microscopy, respectively. Photoluminescent peaks are enhanced significantly with red shifts, and the absorption is broadened to near-infrared, implying a shrinked bandgap after RE co-doping, which is consistent to the calculation results by density functional theory (DFT). The Er3+/Yb3+ co-doped WS2 device demonstrates high carrier mobility, photocurrent, photoresponsivity, external quantum efficiency, and specific detectivity, which are approximately two orders of magnitudes compared with those of the pristine WS2 device. The values of photoresponsivity and specific detectivity approach 4.8 x 10(4) A W-1 and 5.5 x 10(14) Jones, respectively, at 20 V bias and 1.77 mW cm(-2) luminescence, which may refresh the records as has been reported. The excellent performances of the WS2 photodetector prove the effectiveness of Er3+/Yb3+ co-doping for practical application in optoelectronics.