Journal Article

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

Closset, Raphael, Ivanova, Tatyana, Vertruyen, Benedicte, Harizanova, Antoaneta, Koutzarova, Tatyana

2022

Overview

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.

• Publisher: MDPI AG,MDPI
• Subject: Annealing / Band-gap tuning / Chemical elements / Chemistry / Chimie / Comparative analysis / Condensed Matter Physics / Crystallites / Crystallization / Deposition / Dielectric films / Dielectric properties / Doping / Energy gap / Field emission microscopy / film morphology / Fourier transforms / General Materials Science / Glass substrates / Infrared spectroscopy / Investigations / Lasers / Lattice parameters / Magnesium / Materials Science (all) / Mg films / Mg-doped ZnO / Mg-doped ZnO film / Mg-doped ZnO films / Mg-doping / Molecular beam epitaxy / Morphology / optical band gap tuning / Optical properties / Phase transitions / Photocatalysis / Photovoltaic cells / Physical, chemical, mathematical & earth Sciences / Physique, chimie, mathématiques & sciences de la terre / Refractivity / Silicon substrates / Sol'gel / Sol-gel processes / sol–gel technology / Spectrum analysis / Surface structure / Thin films / Wurtzite / Zinc oxide / ZnO films