Effects of ZnO buffer layer thickness on properties of ZnO thin films deposited by radio-frequency magnetron sputtering

A series of ZnO films were deposited on c-plane sapphire substrates having different buffer layer thicknesses between 50 and 500 Å by radio-frequency (rf) magnetron sputtering. Scanning electron microscopy (SEM) was utilized to investigate the surface morphology of ZnO films. The crystallinity of ZnO films was investigated by the double-crystal X-ray diffractometry (DCXRD). The optical properties of ZnO films were also investigated using low-temperature (LT) photoluminescence (PL). It was found that the surface morphology, structural and optical properties of the films depended on the thickness of the buffer layer. The films deposited on the 100 Å thick ZnO buffer layer exhibit the good structural and optical properties with a very smooth surface.