Doping Ga effect on ZnO radio frequency sputtered films from a powder target
Abstract Undoped ZnO and ZnO:Ga films have been radio frequency (RF) sputtered on glass substrates using powder targets. X ray diffraction studies reveal that the films are polycrystalline with a hexagonal wurtzite structure and a preferential orientation along the c axis. The (002) peak shift to lower 2th values indicates that the films suffered compressive stress with Ga incorporation. The grain sizes are found in the range of 20 23 nm showing a nanostructure. All the films are highly transparent 85% in the visible region and the optical band gap shows a blue shift with Ga incorporation up to 3 wt. then a red shift with further Ga content from 3.56 to 3.47 eV due to band tail. Urbach energy increases from 0.06 to 0.15 eV with Ga content revealing disorder increase in the lattice. Besides the near band emission peak, which shows the same trend for the optical band gap variation, Photoluminescence measurements show deep level emissions in the violet, blue and green regions. The electrical parameters were obtained with both optical reflectance based on the Drude free electron model and the Hall method and similar tendencies were observed within the two methods. The highest figure of merit observed in this study was 3.57 x 10 3 O 1 showing that the 3 wt. ZnO:Ga films are potentially attractive for application as transparent conductive oxide thin films in solar cells. RF sputtering from a powder target was found to be a simple and cost effective technique for the synthesis of ZnO thin films for potential applications in the renewable energy devices.