Structural and luminescence properties of sol-gel derived Cu doped ZnO films

Abstract

Well crystallized Cu doped (1, 3 and 5 molar %) ZnO films have been deposited on quartz substrates by sol-gel technique. The microstructural, optical and photoluminescence properties of the films have been studied. It has been observed that the band gap (3.38 eV) of ZnO films did not vary up to 5 molar % of Cu doping. The preferred orientation along (002) was observed for all the films. The X-ray diffraction (XRD) measurement confirmed the decrease of degree of orientation of (002) plane with increasing molar % of Cu in the films. The atomic force microscopy (AFM) measurements have also been performed to examine the surface morphologies of the films. It has been observed that the surface roughness of 1 molar % Cu doped film is smaller (~ 6 nm) than those of 3 and 5 molar % of Cu. The photoluminescence of the films shows prominent peaks between 2.27 to 3.11 eV due to excitonic as well as defect related transitions. A possible mechanism of carrier transitions between shallow and deep impurity levels in the photoluminescence has also been studied.