Investigation of response mechanism for ZnO thin film based surface acoustic wave ultraviolet detector

A ZnO thin film as ultraviolet (UV) illumination sensing layer was deposited through radio frequency magnetron sputtering on the surface acoustic wave (SAW) wavelet device, which was fabricated on the 128°Y-X LiNbO₃ piezoelectric substrate. The characteristics of UV illumination response of the detector were tested and measured using a network analyzer. The experimental results showed that a maximum frequency shift of 37 kHz could be obtained with a 365 nm 210 μW/cm² UV illumination and the detector had a good repeatability. Further, the UV response process and the recovery process both contained a fast period and a slow period. The fast period depended on the adsorption and desorption of oxygen molecules at the surface of ZnO thin film, and the slow period depended on the slow exchange process between the outside oxygen molecules and the native defects inside ZnO crystal. At last, the theoretical formulas for the UV response process and the recovery process were derived by combining the acoustoelectric effect and the photoconductivity effect. The investigation of response mechanism of the ZnO thin film based SAW UV detector with high sensitivity provided suggestions for the improvement of transient characteristics and the practicality of the detector.