Exciton localization and Stokes’ shift in Zn1−xCdxO thin films depending on chemical composition

Zn1−xCdxO films were grown on (0 0 0 1) sapphire substrates by pulsed laser deposition. Structural and optical properties of Zn1−xCdxO films were strongly correlated to the processing conditions. The optical energy band gap of Zn1−xCdxO thin films, measured by photoluminescence and transmittance, changed from 3.248 to 3.291 eV at 275 K. Increase of Cd content also leads to the emission broadening and degraded crystallinity. The absorption edge and ultraviolet emission peak shift to lower energy from 3.291 to 3.248 eV and 3.278 to 3.106 eV, respectively, with increasing Cd content from 0.3% to 3% at 275 K. The Stokes’ shift between the absorption and emission indicates the increase of localization of exciton with Cd content. Stokes’ shift increases with Cd content caused mainly by the localized states in ZnCdO films.