Structure, Piezoelectricity and Optical Properties of ZnO Thin Films Fabricated by Sol-Gel Method

ZnO thin films were prepared on crystal substrate Si (111) by sol-gel technology, then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). The ZnO films characterized by X-ray diffraction are highly oriented in (002) direction with the growing of the l mm thickness. The morphologies, roughness and grain size of ZnO investigated by AFM show that roughness and grain size of ZnO films decrease with the increase of the film thickness. The roughness dimension is 2.188–0.914 nm. The results show that the piezoelectric coefficient increases with the increase of thickness and (002) orientation. When the force reference is close to surface roughness of the films, the piezoelectric coefficient measured is inaccurate and fluctuates in a large range, but when the force reference is big, the piezoelectric coefficient d33 changes little and ultimately keeps constant at a low frequency. The photoluminescence spectrum of the samples has an UV emission peak centred at 383 nm with broad band visible emission centred in the range of 500 - 600 nm.