LAUSR

Abstract Ultrathin zinc oxide (ZnO) films with thickness down to several nanometers have been fabricated by atomic layer deposition. The chemical composition, surface morphology, crystalline structure, optical properties and photoluminescence characteristics of the ZnO films with various thicknesses were investigated. The X-ray photoelectric spectroscopy illustrates that the deposited films are uniformly distributed with zinc and oxygen atoms. Spectroscopic ellipsometric measurements reveal that both the refractive index and extinction coefficient decrease monotonically as the thickness of the film decreases. The thickness of the ZnO films obtained via ellipsometry is consistent with X-ray reflectivity measurements. The excitonic emission peak of the photoluminescence spectrum shifts to higher energies when the film thickness decreases to a few nanometers. This blueshift phenomenon is consistent with the expansion of the fundamental optical bandgap determined from ellipsometry, which could be well described by the effective mass model using physically meaningful parameters. The results obtained in this study could provide guidance to the design and optimization of optoelectronic devices based on ultrathin ZnO films.