Effect of Gd doping on spray pyrolyzed NiO thin films for optoelectronic applications

In the present work, we systematically investigated the effect of Gd (1, 3, and 5%) doping on the structural, morphological, electrical, and optical properties of NiO thin films deposited on glass substrate using the spray pyrolysis method. X-ray diffraction study revealed that the deposited Gd:NiO(0–5%) films exhibit cubic structure with preferred orientation along (111) direction. The average crystallite size decreases from 15 nm to 12 nm with increasing Gd doping concentration. The atomic force microscope (AFM) topography study revealed that there is a decrease in grain size and variation of roughness with increasing Gd content into NiO lattice. The energy-dispersive X-ray spectroscopy (EDX)/ scanning electron microscope (SEM) mapping studies show the presence and uniform distribution of Gd in the Gd:NiO films. The average optical transparency (70%) and the optical band gap energy values decrease in Gd doped NiO films. The refractive index values are found to be in the range of 1.5–2.6. The higher values of linear and nonlinear optical parameters like χ₁, χ₃ and n₂ are found to be 0.98 esu, 3.31 × 10⁻¹⁰ esu and 2.92 × 10⁻⁹ esu, respectively in Gd doped NiO films. The current study indicates that the Gd doping concentration has a strong influence on linear and non-linear optical properties of NiO films and makes them useful in several optoelectronic device applications.