Quantum confinement effects of thin ZnO films by experiment and theory

Thin ZnO films with thickness ranging between 2 and 300 nm have been grown on quartz, Corning glass and Si(100) substrates by radio frequency magnetron sputtering. The film thickness was determined by pre-calibrated quartz balance with the help of x-ray reflectivity measurements. X-ray diffraction experiments revealed the formation of highly-textured hexagonal ZnO. Ultraviolet–visible light absorption spectroscopy has shown a “blue shift” of the direct band gap of ZnO. The experimental results are interpreted as evidences of quantum confinement effects. This is supported by theoretical predictions of the optical gap, which was calculated in the framework of effective mass approximation by solving the two particle (electron and hole) Hartree-Fock equations. The observed fair agreement between theoretical and experimental results corroborates the quantum confinement interpretation. •Thin ZnO films with thickness ranging between 2 and 300 nm have been grown by radio frequency magnetron sputtering.•The film thickness was determined by pre-calibrated quartz balance with the help of x-ray reflectivity measurements.•Ultraviolet–visible light absorption spectroscopy has shown a “blue shift” of the direct band gap of ZnO.•The experimental results are supplemented by theoretical calculations.•The agreement between theoretical and experimental results corroborates the quantum confinement interpretation.