Enhanced performance of self-powered CuS photodetectors with Al doping and dark current suppression

In this study, un- and aluminum (Al)-doped copper sulfide (CuS) nanostructures were synthesized using the sonochemical method and employed as a photodetector. The physical properties were characterized through Xray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis-NIR absorption, photoluminescence (PL), and Raman spectroscopies. The CuS nanostructures exhibited a polycrystalline covellite structure. Al doping, at different concentrations, influenced the crystallite size, with a reduction at lower concentrations and an increase at higher concentrations. Transmission electron microscope images revealed that Al doping led to an increase in the average size of CuS nanostructures. Elemental analysis indicated Cu-poor stoichiometry, which was intensified with higher Al concentrations. Evaluation of electrical properties showed that all samples exhibited dominant hole (p-type) electrical conductivity. Moreover, in Al-doped CuS nanostructures, both the carrier density and diode coefficient increased compared to the undoped sample. Photodetectors fabricated with CuS nanostructures demonstrated that Al doping suppressed dark current and enhanced photocurrent.