Ellipsometric studies of nickel oxide thin films synthesized via spray pyrolysis at varied substrate temperatures for optoelectronic applications

Abstract

Abstract The impacts of the substrate temperature on diverse microstructural, morphological, and optical features of the nickel oxide films deposited via spray pyrolysis were examined. The X-ray diffraction patterns revealed a dominant peak with (1 1 1) favored orientation for all the deposited samples. As the temperature went up from 350 to 450 °C, the indirect and direct band gap energies increased between 2.65 and 2.77 eV and from 3.80 to 3.89 eV, respectively. The thickness and the optical constants of the nickel oxide were estimated by fitting the measured Psi and Delta parameters by adopting a suitable optical model based on B-splines in the wavelength range of 380–900 nm. We obtained that the refractive index significantly decreased from 1.717 to 1.59. But, the extinction coefficient substantially augmented from 0.383 to 0.515. Furthermore, the values of the average oscillator and the dispersion energies were estimated by utilizing the Wemple-DiDomento model. At last, there was a correlation between the different sizes of the crystallite and the optical parameters of the nickel oxide thin films. The optical band gap increased while the refractive index and Urbach energy reduced with a rise in crystallite size.