Abstract

Using spectroscopic ellipsometry from the midinfrared (0.03eV) to the deep ultraviolet (6.5eV), the authors determined the thickness dependence of the dielectric function for ZnO thin layers (5-50nm) on Si and quartz in comparison to bulk ZnO. They observed a small blueshift of the band gap ( similar to 80meV) in thin ZnO layers due to quantum confinement, which is consistent with a simple effective mass theory in an infinite potential well. There is a drastic reduction in the excitonic effects near the bandgap, especially for thin ZnO on Si, which not only affects the excitonic absorption peak but also lowers the high-frequency dielectric constant by up to 40%. No significant change of the phonon parameters (except an increased broadening) in thin ZnO layers was found.