Effects of misfit strain on properties of ZnO films grown by pulsed laser deposition

A series of ZnO films with various thicknesses were prepared on (0001) sapphire substrate by pulsed laser deposition (PLD). Scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis were utilized to investigate the effects of misfit strain on the surface morphology and the crystallinity. The electrical and optical properties of the films were also investigated as a function of the film thickness. It was found that the crystalline quality, electrical and optical properties of the films depended on the film thickness and were improved with increasing the film thickness. This is attributed to the fact that the films thinner than 400 nm are under the severe misfit strain, which decreases as the film thickness increases further.