Preparation, characterization and optical properties of nanostructured undoped and Cu doped ZnO thin films

In this work, undoped and Cu-doped ZnO (ZnO:Cu) nanostructured thin films were synthesized by chemical bath deposition method. UV-Visible and photoluminescence (PL) spectroscopy have been used to investigation of optical properties of the samples in detail. The band gap energy of undoped and Cu-doped ZnO films is blue-shifted by approximate to 0.3 eV with respect to the bulk value (3.37 eV), probably due to the quantum size effect as expected from the nanocrystalline nature of the films. The photoluminescence (PL) spectra of the ZnO: Cu thin films exhibited two emission peaks, one blue peak located at 491 nm and a intense deep level-green peak at 521 nm. The intensity of photoluminescence emission is enhanced with increasing Cu concentration and deposition temperature. The intensity of peaks is optimized at Cu: Zn ratio of 0.29% for the ZnO: Cu thin films. Fourier transform infrared (FTIR) spectroscopy shows two peaks in 427.22 and 532.71 cm(-1) which is attributed to ZnO and CuO bonds, respectively. The x-ray diffraction and scanning electron microscopy techniques indicated that the films have hexagonal phase of ZnO.