Structural and optical properties of ZnO thin films prepared by sol–gel method with different thickness

▶ It is found that the thickness has a great effect on the structural and optical properties of ZnO thin films deposited from sol-gel method. ▶ With the increase of film thickness, both the crystalline quality and ultraviolet emission of ZnO thin film are gradually improved. ▶ The growth process of highly c-axis oriented ZnO thin films prepared by sol-gel method is a self-template process. ▶ With the increase of film thickness, a growth mode from vertical growth to lateral growth is found and the transition point is between 270 and 360nm thickness. In this work, ZnO thin films with different thickness were prepared by sol–gel method on glass substrates and the structural and optical properties of these films were studied by X-ray diffractometer, atomic force microscope, UV–visible spectrophotometer, ellipsometer and fluorophotometer, respectively. The structural analyses show that all the samples have a wurtzite structure and are preferentially oriented along the c-axis perpendicular to the substrate surface. The growth process of highly c-axis oriented ZnO thin films derived from sol–gel method is a self-template process. With the increase of film thickness, the structural disorder decreases and the crystalline quality of the films is gradually improved. A transition of crystal growth mode from vertical growth to lateral growth is observed and the transition point is found between 270 and 360nm thickness. The optical analyses show that with the increase of film thickness, both the refractive index and ultraviolet emission intensity are improved. However, the transmittance in the visible range is hardly influenced by the film thickness, and the averages are all above 80%.