Deposition of Sol–Gel ZnO:Mg Films and Investigation of Their Structural and Optical Properties

Abstract

This work presents a facile sol–gel method for the deposition of ZnO and ZnO:Mg films. The films are spin coated on silicon and quartz substrates. The impact of magnesium concentrations (0, 0.5, 1, 2 and 3 wt%) and post-annealing treatments (300–600 °C) on the film’s structural, vibrational and optical properties is investigated. Undoped ZnO films crystallize in the wurtzite phase, with crystallite sizes ranging from 9.1 nm (300 °C) to 29.7 nm (600 °C). Mg doping deteriorates the film crystallization and shifting of 002 peak towards higher diffraction angles is observed, indicating the successful incorporation of Mg into the ZnO matrix. ZnO:Mg films (2 wt%) possess the smallest crystallite size, ranging from 6.2 nm (300 °C) to 25.2 nm (600 °C). The highest Mg concentration (3 wt%) results into a segregation of the MgO phase. Lattice constants, texture coefficients and Zn–O bond lengths are discussed. The diminution of the c lattice parameter is related to the replacement of Zn2+ by Mg2+ in the ZnO host lattice. The vibrational properties are studied by Fourier transform infrared (FTIR) spectroscopy. IR lines related to Mg–O bonds are found for ZnO:Mg films with dopant concentrations of 2 and 3 wt%. The optical characterization showed that the transmittance of ZnO:Mg thin films increased from 74.5% (undoped ZnO) to about 89.1% and the optical band gap energy from 3.24 to 3.56 eV. Mg doping leads to a higher refractive index compared to undoped ZnO films. The FESEM (field emission scanning electron microscopy) technique is used for observation of the surface morphology modification of ZnO:Mg films. The doped ZnO films possess a smoother grained surface structure, opposite to the wrinkle-type morphology of undoped sol–gel ZnO films. The smoother surface leads to improved transparency of ZnO:Mg films.

An in-depth look at the structural, electronic, optical, and thermal properties of the cubic Be x Mg y Zn1−x−y O quaternary alloys

“…Specifically, the bandgap values were determined to be 4.05 eV, 5.11 eV, and 5.24 eV for the compositions (x, y) of (0.25, 0.25), (0.25, 0.50), and (0.50, 0.25), respectively. The findings from experimental research provide confirmation that the bandgap of ternary alloys, specifically BeZnO and MgZnO, and the quaternary alloy BeMgZnO increases as the concentration of Be and Mg atoms incorporated into the ZnO host structure increases [53,[55][56][57][58]. Hence, as depicted in figures 4(a)-(c) and figure 6(a), it can be observed that the bandgap of these alloys exhibits an upward trend as the composition increases.…”

“…In general, there is a rise in the bandgap values as the composition increases. The recent work of Ivanova [55] showed that the optical bandgap energy of ZnMgO thin films increase from 3.24 to 3.56 eV, and the results clearly reveal that Mg incorporation enlarges the optical bandgap. These results are also confirmed by Siregar [56].…”