Effects of growth temperature of MBE-seed layers on the structural and optical properties of ZnO thin films prepared by using the sol-gel method

ZnO thin films on molecular beam epitaxy (MBE) seed layers/Si (111) substrates were prepared by using the sol-gel method. The seed layers were grown at various growth temperatures ranging from 300 to 900°C. Atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) measurements were carried out to investigate the effects of the seed layers' growth temperature on the properties of the ZnO thin films. The grains of the seed layers become larger and rougher as the growth temperature is increased. The surface morphologies of the ZnO thin films are changed from elliptical to spherical and the particle size of the ZnO thin films surface is decreased as the growth temperature is increased. The (002) diffraction peaks for ZnO thin films with seed layers are observe to be higher and narrower compared to those of the ZnO thin films without a seed layer. Especially, the ZnO thin films on seed layers grown at a low growth temperature (300°C) exhibit the largest enhancement among the ZnO thin films with seed layers. In contrast to the XRD results, the PL intensity ratio of the ZnO thin films gradually increases as the growth temperature is increased due to an increase in the quantum efficiency attributed to the change in the surface morphologies of the ZnO thin films.