Spectroscopic ellipsometry and morphological studies of nanocrystalline NiO and NiO/ITO thin films deposited by e-beams technique

The current article reported a new data on the structural, surface morphology and optical properties of multi-thickness nanocrystalline NiO/glass substrate and NiO/ITO/glass substrate semiconductor thin films prepared by electron beam deposition technique. Structural investigation shows that the as-deposited multi-thickness NiO films deposited on a glass substrate crystallize in the form of cubic NaCl type structure. However, ITO thin film has a cubic type structure. Besides, the increase in the crystallite size was observed with increasing the thickness of NiO film, this behavior was confirmed by AFM micrographs. In the spectral range 280 nm–1800 nm, the optical properties of the NiO/glass substrate and NiO/ITO/glass substrate thin films have been investigated using spectroscopic ellipsometry (SE) technique. For NiO/glass substrate sample, the SE results providing direct energy Egdir≈ 3.954 eV, indirect energy Egindir≈ 2.855eV and phonon energy of order 200 meV. In addition, the analysis of the refractive index dispersion gives the atomic number density to be Nfij=2.213x1022cm−3. On the other hand, for the NiO (410 nm)/ITO (99 nm)/glass substrate thin film sample, a reduction in the direct transition energy to Egdir≈ 3.24eV and also in the factor Nfij to 1.6x1022cm−3was observed. Additionally, the values of the oscillator parameters were calculated for NiO/glass substrate and NiO/ITO/glass substrate thin films using the Wemple-DiDomenico single oscillator model (WDD). Finally, it was found that the values of Urbach energy for NiO/glass substrate and NiO (410 nm)/ITO (99 nm)/glass substrate are very small relative to the energy gap values which indicates that the region of localized sates is very narrow compared to the width of the energy gap.