Epitaxial growth of highly transparent and conducting Sc-doped ZnO films on c-plane sapphire by sol-gel process without buffer

Highly transparent and conductive scandium doped zinc oxide (ZnO:Sc) films were deposited on c-plane sapphire substrates by sol-gel technique using zinc acetate dihydrate [Zn(CH3COO)2·2H2O] as precursor, 2-methoxyethanol as solvent and monoethanolamine as a stabilizer. The doping with scandium is achieved by adding 0.5 wt% of scandium nitrate hexahydrate [(ScNO3·6H2O)] in the solution. The influence of annealing temperature (300-550 °C) on the structural, optical and electrical properties was investigated. X-ray Diffraction study revealed that highly c-axis oriented films with full-width half maximum of 0.16° are obtained at an annealing temperature of 400 °C. The surface morphology of the films was judged by SEM and AFM images which indicated formation of grains. The average transmittance was found to be above 92% in the visible region. ZnO:Sc film, annealed at 400 °C exhibited minimum resistivity of 1.91 × 10−4 Ω cm. Room-temperature photoluminescence measurements of the ZnO:Sc films annealed at 400 °C showed ultraviolet peak at ∼3.31eV with a FWHM of 11.2 meV, which are comparable to those found in high-quality ZnO films. Reflection high-energy electron diffraction pattern confirmed the epitaxial nature of the films even without introducing any buffer layer.