Study on the performance of ZnO nanomaterial-based surface acoustic wave ultraviolet detectors

A ZnO nanomaterial-based surface acoustic wave (SAW) ultraviolet (UV) detector is highly desirable for UV radiation detection due to its high sensitivity. In this work, firstly the ZnO nanomaterial-based SAW UV detectors operating at three different frequencies (∼50, ∼100 and ∼200 MHz) were fabricated. Then, four ZnO nanomaterial sensing layers with different thicknesses were synthesized on the SAW UV detectors operating at ∼200 MHz. The morphology, crystallization and photoluminescence of ZnO nanomaterial sensing layers were characterized using the scanning electron microscopy, transmission electron microscopy, x-ray diffraction and fluorescence spectrometer, respectively. The SAW UV detectors based on different operating frequencies and ZnO nanomaterial sensing layer's thicknesses were exposed under UV illumination at a wavelength of 365 nm and their UV responses were measured. The experimental results indicate that the frequency shift of ZnO nanomaterial-based SAW UV detector can be significantly improved by increasing operating frequency or ZnO nanomaterial sensing layer's thickness. Furthermore, the detectors exhibit good selectivity of UV illumination, an ultrahigh UV sensitivity of about 9.6 ppm (W cm^-2)^-1 and fast transient properties. The experimental results agree well with the acousto-electric effect theory. What deserves to be noted is that, under a UV intensity of 150 W cm^-2, the frequency shift of the SAW UV detector operating at ∼50 MHz with a thin ZnO nanomaterial sensing layer was only ∼50 kHz while that of the SAW UV detector operating at ∼200 MHz with a thick ZnO nanomaterial sensing layer could reach ∼292 kHz. These results suggest the huge potential applications of ultra-sensitive ZnO nanomaterial-based SAW UV detectors for remote wireless UV and radiation monitoring.