  Zinc oxide (ZnO) epitaxial thin films grown on c-sapphire substrates by
pulsed laser deposition were investigated using angle and polarization-resolved
photoluminescence spectroscopy. Side-emission spectra differed significantly
from surface-emission spectra in exhibiting dominant, narrow,
polarization-resolved peaks. These spectral features were attributed to leaky
substrate modes in the layers. Observations were first verified using
transmission calculations with non-adjustable parameters, which took into
account the dispersion, the anisotropy of the ZnO refractive index and the
dependence on film thickness. Results were consistent with Fabry-Perot-like
interference being the origin of the distinctive ZnO luminescence observed at
grazing incidence angles. A second analysis, based on the source terms method,
was used in order to retrieve the bulk emission properties, including the
wavelength-dependent quantum yield and the emission anisotropy. While ZnO thin
films were considered here, this analysis method can be extended to any
luminescent thin film of similar geometry, demonstrating the potential of leaky
mode analysis for probing passive and active material properties.
