Effect of Na-doped Concentration on the Structure and Optical Properties of ZnO Thin Films

Na-doped ZnO thin films were deposited on microscope glass substrates by sot-gel spin coating method, the Na/Zn ratio were 0at.%, 5at.%, 7.5at.%, 10at.%, 15at.%. The crystal structures, surface morphology, and optical properties were analyzed by X-ray diffraction, scanning electron microscopy, ultraviolet visible spectrophotometer, respectively. The results show that all the films are preferentially oriented along the c-axis perpendicular to the substrate surface. With the increase of the doping concentration, the roughness of the surfaces decrease and grain size grows from 17.1nm to 21.7nm, the sample with 10at.% Na exhibits best crystallinity and has lowest strain along the c-axis. The average optical transparency of the samples is higher than 70%, optical band gaps are between 3.213eV and 3.289eV.