Synthesis and characterization of zinc oxide thin films for optoelectronic applications

Abstract

Micro-ring structured zinc oxide (ZnO) thin films were prepared on glass substrates by spray pyrolysis and their structural, morphological, optical and electrical properties were investigated. X-ray Diffraction (XRD) analysis revealed the films’ hexagonal wurtzite phase with a preferred (002) grain orientation. The mean crystallite size calculated on the basis of the Debye-Scherrer model was 24 nm and a small dislocation density of 1.7×10−3 nm−2 was obtained, indicating the existence of few lattice defects and good crystallinity. Scanning Electron Microscopy (SEM) micrographs revealed the film’s granular nature composed of rod-shaped and spherical nanoparticles which agglomerated to form micro-ring like film clusters on the film surface. The average transmittance in the visible region, optical band gap and Urbach energy were approximately 75–80%, 3.28 eV and 57 meV, respectively. The refractive index and extinction coefficient were determined using Swanepoel’s envelope method. Raman spectroscopy revealed the presence of small amounts of residual tensile stress and low density of defects in the ZnO thin films. This was consistent with XRD analysis. A low sheet resistivity (6.03×101 normalΩcm) and high figure of merit (4.35×10−6 Ω−1) were obtained for our films indicating their suitability in optoelectronic applications.

Effect of annealing temperature on structural morphological and optical properties of spray pyrolized Al-doped ZnO thin films

“…The dislocation density and strain values of the film have been found to decrease with the increase of annealing temperature up to 450°C and then increases. This tendency indicates that annealing reduces the lattice defects of the films and increases the crystalline quality by modifying the periodic arrangements of atoms in the crystal lattice [1,2,18,19]. The dislocation density and strain value show a reverse relation when the films are annealed above 450°C i.e.…”

“…So, the absorption edge shifts from the lower to higher wavelength with annealing, which indicates the increase of optical transmittance. Many researcher reports that the film had an average transparency 75% in the visible region which may be associated with the film's good structural homogeneity and crystallinity and this is good for optical device application [2,14,21].…”

“…Transparent conducting oxides (TCO) materials have attracted significant research attention in the recent years due to their potential applications in optoelectronic devices such as in gas sensors, piezoelectric transducers, touch screens, liquid crystal displays, light emitting devices and in solar cells [1,2]. So far, indium tin oxide (ITO) was a typical commercial TCO.…”

“…The most explored deposition techniques include spray pyrolysis, chemical vapor deposition, sputtering, reactive evaporation, pulsed laser ablation, spin coating, dip coating, hydrothermal method etc [7]. Out of these, spray pyrolysis is of particular interest due to its inexpensive cost, simplicity, no high vacuum requirement, safety, less waste production and capability of coating large areas [2]. In this research work, 2 wt% Al-doped ZnO thin films has been fabricated by spray pyrolysis technique.…”

Effect of polyethylene glycol and propyltrimethoxysilane on structural and optical properties of zinc oxide nanoparticles synthesized by sol–gel process

“…In the last few years, there has been a growing interest of the researchers, focusing on the synthesis of nanocrystalline ZnO, hence, many methods, including sol-gel [6][7][8][9]. Thereby, particle size and crystal morphology play important roles in all applications, like nanodevices for opto-electronic [10], gas sensing [11], photocatalytic activity [12]. A part of the technological meaning of zinc oxide nanoparticles (ZnO NPs), their diameters ranging from 10 to 100 nm make them good-looking from academic point of view [13].…”