Abstract
Distinct transitions due to free excitons in ZnO epitaxial films are observed at 3.5 K. With rise in temperature, the emission intensity of free excitons increases relative to that of bound excitons and dominates the spectrum over 60 K. These results demonstrate the good quality of the film. From these ZnO films, phonon-assisted emissions associated with transitions of free excitons are observed. The temperature dependence of the peak position of the phonon replicas is found to follow theoretical predictions, as demonstrated in ZnO bulk.