Linear and nonlinear optical investigations of N:ZnO/ITO thin films system for opto-electronic functions

Abstract

Different concentrations of N (0, 1, 3 and 5 wt.%) added ZnO thin films were primed using spin coater. X-ray diffraction (XRD) patterns confirm the preferred growth orientation of all films along (0 0 2) plane, however, ITO has dominant features owing to low thickness of the films. XRD along with vibrational spectroscopy confirms the single hexagonal phase of ZnO. The crystallite size evaluated from Scherrer's equation increased with increase in N-doping concentrations and is found to lie in the range of 25–36 nm. The increased crystallite size reduces the dislocation density which confirms the reduction of defects in the films. The dislocation density (δ) is found to be 1.569, 1.369, 0.984, and 0.965 for 0, 1, 3 and 5 wt.% N doped ZnO films. N doping in ZnO was confirmed by EDX analysis and its homogeneous distribution was further confirmed by SEM mapping. AFM study confirms the formation of spherical nanoparticles whose size increase with increase in N doping, validating the XRD results. The films are found to have ∼80% transparency which is quite impressive from window layer application point of view. Absorption edge is found to be red shifted owing to N doping, indicating a reduction in energy gap. Hence energy gap was evaluated using Tauc's relation and is found to reduce from 3.43 to 3.14 eV (ΔE = 0.29 eV) with in content of N-doping. The absorption index, refractive index, real and imaginary dielectric constants were also estimated. The values of χ(1) and χ3 are estimated to be in range of 0.3–9 and 1.0 × 10−11 - 1.0 × 10−8, respectively. The Nanocrystalline films with spherical nanocrystallites, high optical transparency and non-linear properties recommend their application in opto-electronic technology.