Abstract
The ZnO films were prepared by reactive rf-magnetron sputtering on silicon and sapphire substrates. For Cu-doping of the ZnO films, the close space sublimation method (CSS) was used at atmospheric pressure in air. After CSS processing, the ZnO and ZnO-Cu films were annealed in a wet media. The reference ZnO-Cu films, obtained from ZnO-Cu target by electron-beam evaporation (EBE) were treated at the same conditions. The microstructure and optical properties of the samples were compared and studied by atomic force microscopy (AFM), X-ray diffraction (XRD), photoluminescence (PL) and cathodoluminescence (CL) spectra. XRD results indicated that all the ZnO films have a polycrystalline hexagonal structure. The surface and crystal quality of ZnO thin film was improved when doped with Cu. The shape of the spectrum depends on the method of doping. Spectrum of the reference ZnO-Cu films has green band only. Spectrum of ZnO-Cu films consists of three emission bands at doping by CSS. The first band is in a blue region with a maximum at 465 nm. The second and third bands are in the green and orange regions with maximum at 520 and 580-600 nm, respectively. The green band is the most intensive. As a consequence, the emission looks like white light. Origin of observed emission bands is discussed.
Highlights
Zinc oxide is a promising material for a variety of practical applications as a transparent conductive electrode, heterojunction laser diode, ultraviolet (UV) laser, luminescent material, etc. [1]
X-ray diffraction (XRD) measurements showed that all ZnO films have a polycrystalline hexagonal structure
The surface morphology modification caused by doping process was investigated by atomic force microscopy (AFM) since an introduction of the Cu impurity by close space sublimation (CSS) methods is based on the diffusion of Cu ions into the films through the grains or grain boundaries
Summary
Zinc oxide is a promising material for a variety of practical applications as a transparent conductive electrode, heterojunction laser diode, ultraviolet (UV) laser, luminescent material, etc. [1]. Beneficial effect of water vapor on growth of ZnO crystals and on structural properties of ZnO films is well known for a long time [18, 19, 20]. This method represents favorable condition at appropriate temperature for the impurity to be effectively introduced into ZnO film. The present work was aimed to investigate the effect of Cu doping by CSS technique on structure and luminescent properties of ZnO thin films
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