Carbon enhanced blue–violet luminescence in ZnO films grown by pulsed laser deposition

Five Zinc oxide thin-films were prepared by pulsed-laser deposition (PLD) using a ceramic ZnO target and a KrF excimer laser. The samples were all deposited on c-axis sapphire at different ambient oxygen pressures. They were then characterized using ellipsometry, atomic-force microscopy (AFM), photoluminescence (PL) spectroscopy, Rutherford backscattering spectroscopy (RBS), and nuclear reaction analysis (NRA).Along with the characteristic band-edge (3.36 eV) and deep level (2.3 eV) PL features, strong blue/violet emissions around 3 eV were also observed and are generally attributed to zinc vacancies and zinc interstitials. NRA reveals carbon impurities in all samples and the introduction of more carbon impurities enhanced the blue/violet emissions and inhibited the green luminescence. It is concluded that the carbon impurities promote the zinc related native defects in ZnO and may also be radiative centers in the violet part of the spectrum.