Influence of Magnesium Content on the Structural, Optical, and Electrical Properties of Cu₂(Zn_1-xMg_x)SnS₄ Nanostructured Quaternary Thin Film Synthesized Using the Sol–Gel Method

Nanostructured Cu₂ZnSnS₄ (CZTS) and Cu₂(Zn_1-xMg_x)SnS₄ quaternary alloys with varying magnesium (Mg) content were synthesized using a low-cost, environmentally friendly co-precipitation technique. The structural characteristics of Cu₂(Zn_1-xMg_x)SnS₄/Si were analyzed using x-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The XRD results showed that the CZTS film crystallized the kesterite phase, whereas the Cu₂MgSnS₄ film formed a stannite phase. Increases in Mg content led to an increase in the crystallinity of the deposited alloy, and to an increase in the average crystallite size from 31.65 nm to 53.73 nm. FE-SEM micrographs indicated the morphology of more densely packed nanostructures with less porosity when the Mg content was increased, resulting in the granular structure changing to a whisker-like form. Investigation into the optical properties of photoluminescence spectra revealed a decrease in the band gap of the Cu₂(Zn_1-xMg_x)SnS₄ film from 1.71 eV to 1.67 eV when the Mg content was increased from 0 wt.% to 1 wt.%. The current–voltage characteristics demonstrated that the prepared alloys exhibited ohmic behavior and the photocurrent improved from 1.69 × 10^–4 to 2.86 × 10^–4 A as the Mg content increased from 0 wt.% to 1 wt.% at an applied voltage of 6 V. The highest photosensitivity and photocurrent responsivity of the produced Cu₂(Zn_1-xMg_x)SnS₄ quaternary alloy were 5309% and 2319%, respectively, when the Mg content was 0.7 wt.%, providing the best content for ultraviolet light detection applications.