Evolution of microstructure and photoluminescence of ZnO thin films irradiated with 3 MeV alpha particles

Abstract The effects of irradiation with 3 MeV alpha particles on the microstructure and photoluminescence (PL) emission of ZnO thin films were investigated as a function of exposure time between 100 s and 8 h. The analysis of atomic force microscopy (AFM) data reveals modifications of the surface morphology when the irradiation periods exceed 500 s. The roughness of the films exposed for 500 s and 1000 s slightly decreases. The surface becomes almost flat after 8 h irradiation, showing a small density of randomly distributed large aggregates, increased crystallite size and reduced lattice strain and residual stress. The PL spectra of pristine ZnO films present the main characteristic emission bands at 3.25 eV and 2.75 eV. The emission band at 2.75 eV is quenched after irradiation for 100 s, but recovers constantly for irradiation times increasing to 500 s and 1000 s. New emission bands appear at 2.80 eV in the PL spectra of the films exposed to radiation for 500 s, and at 3.10 eV, 3.00 eV, 2.66 eV and 2.64 eV, when the irradiation time increases to 1000 s. The time evolution of radiation induced defects is discussed in relationship with the PL data, the morphology of the films and details of first principles electronic structure of defective models.