Modification of Orientation, Surface and Optical Properties of ZnO Films by Cesium and Erbium Codoping Using Sol-Gel Method

Highly transparent cesium and erbium codoped ZnO thin films were deposited on glass substrate by spin coating method. Structural, surface and optical properties of films were discussed as a function of doping concentration and annealing temperature. The films have hexagonal wurtzite structure and are preferentially oriented along the a-axis (non-polar) parallel to the substrate surface at a desired annealing temperature. The texture co-efficient values confirm the strong a-axis orientation and the average crystallite size are found to be 31.94 nm. The stress relaxation in ZnO lattice by the substitution of codopant is calculated. From the atomic force microscope (AFM) images, spherical shape grains and wrinkle structures are identified on the codoped film surfaces and reduction of grain size is observed with the increase of doping percentage. Reduction of surface roughness (31-13 nm) of the films is observed. Interstitial zinc related violet emission at 2.83 eV and O-antisite related emission at 2.98 eV observed from photoluminescence spectra. The average optical transmittance in the entire visible region was higher than 90% for all the films.