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

Abstract

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 E g d i r ≈ 3.954 eV, indirect energy E g i n d i r ≈ 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 N f i j = 2.213 x 10 22 c m − 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 E g d i r ≈ 3.24eV and also in the factor N f i j to 1.6 x 10 22 c m − 3 was 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. • The D/nm of NiO film increase from 16.86 to 22.75nm and for NiO/ITO from 15 to 26nm with increasing thickness from 75 to 410nm. • Good correlation between the increase in D/nm and reduction of dislocation density (δ) is found. • SE provides E g d i r ≈ 3.954 eV, E g i n d i r ≈ 2.855eV and E phon 200meV. For NiO/glass film a reduction in E g d i r to 3.24eV for the NiO(410nm)/ITO (99 nm)/glass. • The refractive index of NiO film is independent of the film thickness and atomic number density is found to be N f i j = 2.213 x 10 22 c m − 3 • The values of E o = 6.828eV, E d = 19.3eV for NiO film and E o = 4.56eV, E d = 15.1eV for (410 nm)/ITO (99nm)/glass substrate film are found.