Extraordinary near-band-edge photoluminescence in the highly epitaxial ZnO films deposited by PLD

Highly epitaxial ZnO films deposited on c-plane sapphire substrate by pulsed laser deposition exhibited enhanced extraordinary spectral features in the near-band-edge region, which were studied in comparison with the annealed sample and the bulk ZnO crystal. Based on the characterization in structure and photoluminescence, the near-band-edge emission was assigned to the tail-state luminescence due to the exciton localization, which is different from the bound excitons, instead has the continuous density of states at the deeper levels, probably created by the defects, chemical disorders, and the lattice strains.