Enhancing low-temperature sensor applications: Synergistic effects of Ni doping and SnO2 interlayer on spin-coated ZnO thin films on glass substrate

This study investigates the effects of Nickel doping and a SnO₂ interlayer on the structural, morphological, optical, and electrical properties of ZnO thin films. Undoped and Ni-doped ZnO films were fabricated on glass substrates, with and without an SnO₂ interlayer, using the sol-gel spin coating method. The samples—denoted as ZG (undoped ZnO), NZG (Ni-doped ZnO), ZSG (undoped ZnO with SnO₂ interlayer), and NZSG (Ni-doped ZnO with SnO₂ interlayer)—underwent comprehensive characterization via XRD, AFM, PL, UV–Vis spectroscopy, Hall effect measurements, Hot probe, and Two-point method. XRD analysis confirmed successful Ni incorporation and enhanced ZnO crystallinity, particularly in the presence of the SnO₂ interlayer. AFM analysis revealed improved grain distribution and size due to the synergistic effects of Ni doping and the SnO₂ interlayer. UV–Vis results indicated significant impacts on transparency and the Urbach energy, with Ni doping alone broadening the bandgap. PL measurements showed that the synergistic effects quenched UV luminescence associated with the glass substrate, enhancing visible luminescence. Chromaticity analysis suggested that ZSG and NZSG samples are suitable for warm blue region applications. Electrical measurements revealed n-type conductivity across all films except NZG, with Ni doping increasing resistivity. Additionally, the ZSG (PTC) sensor exhibited a slightly higher sensitivity (0.3852 Ω/°C) compared to the NZSG sensor (0.3782 Ω/°C), with a similar trend observed in NTC sensors. These findings suggest that Ni-doped ZnO films with SnO₂ interlayers could potentially serve as thermistors and RTDs, offering promising applications in temperature sensing and optoelectronics.