Highly sensitive hexagonal-shaped ZnS–Cu thin films for photo-detector applications

In this work, structural, optical, and photoconductivity properties of pure and Cu (1, 2, and 3%)-doped ZnS thin films fabricated by the spray pyrolysis method are reported. X-ray diffraction study reveals the standard hexagonal wurtzite ZnS structure of all the films. E1 (LO) phonon mode centered at 348 cm⁻¹ in Raman spectra further corroborates the wurtzite ZnS nature of all the films. Optical absorbance results suggest the semiconducting behavior of all the films. ZnS thin film shows the optical bandgap energy (E_g) of 3.30 eV, which decreases to 2.95 eV for ZnS:Cu (2%) thin film. Sensitivity parameters: responsivity (R) and the external quantum efficiency (EQE) as well as detectivity (D^*) parameter of Cu (0, 1, 2, and 3%)-doped ZnS photo-detectors increase with increasing Cu content upto 2%, followed by a decrement in these values at the higher Cu-doping content of 3%. ZnS:Cu (2%) photo-detector exhibits the highest R, EQE, and D^* values of 2.24 × 10⁻²AW⁻¹, 7.23% and 2.66 × 10¹⁰ Jones, respectively, among all the fabricated photo-detectors. Thus, the present study reveals the significance of Cu-doping into the ZnS lattice on optical and photoconductivity properties of ZnS thin films.