Ultraviolet sensing based on nanostructured ZnO/Si surface acoustic wave devices

Abstract

Ultraviolet (UV) sensor based on nanostructured ZnO/Si Surface Acoustic Wave (SAW) devices is studied in this paper. The ZnO films sputtered onto Si (100) substrate showed a preferred (0002) orientation and good photoluminescence emission. For the SAW device with a wavelength of 64 m, a frequency downshift of ~ 1.4 kHz was observed at the Rayleigh mode under a UV light intensity of 0.6 mW/cm 2 , whereas the frequency downshift for the Rayleigh mode was increased to 8.3 kHz after integrating ZnO nanorods (NRs) in the ZnO/Si SAW devices. For the SAW device with a wavelength of 20 m irradiated under a UV light intensity of 0.6 mW/cm 2 , a frequency downshift of 25 kHz for the Sezawa mode was obtained compared to a shift of 12 kHz for the Rayleigh mode. After depositing ZnO NRs, the resonant frequency for the Rayleigh mode was increased to 27.4 kHz under the same UV intensity illumination, due to the significant increase in surface-to-volume ratio.

Shear-horizontal surface acoustic wave characteristics of a (110) ZnO/SiO2/Si multilayer structure

“…Surface acoustic wave (SAW) devices have been in commercial use (such as communications, automotive and environmental sensing) for more than 60 years [1][2][3][4][5][6].…”

Surface acoustic wave-based ultraviolet photodetectors: a review

“…These parameters are largely related to the type and quality of the sensing and piezoelectric materials used and the type of sound wave used. In piezoelectric materials, higher mode acoustic waves [41][42][43][44][45][46] or higher values of the electromechanical coupling coefficient k eff 2 [32,39,47-50] are more likely to lead to higher photosensitivity (Eqs. (1), (2) and (3)).…”

“…(1), (2) and (3)). For the sensing materials, nanomaterials such as nanorods, nanobelts and nanowires with large specific surface areas will absorb more UV photons, which will result in higher photosensitivity [32,39,41,[48][49][50][51]55]. It is generally believed that differences in the surface defect concentration caused by annealing will lead to changes in the response time.…”

“…The Sezawa wave is generally induced at a specific thickness of approximately hk = 1 for the first Sezawa mode and only those with high crystalline quality and a large electromechanical coupling coefficient can excite Sezawa waves with hk < 1 [65]. While Sezawa wave generation is affected by certain conditions, the high electromechanical coupling coefficient [64] and high photosensitivity of these waves have attracted extensive research attention, particularly for ZnO [41,42,44].…”

“…Various methods have been used to synthesize ZnO nanomaterials. The material structures include ZnO nanowires [39,48,49], nanorods [41,44,51], nanoparticles [32], nanobelts [72] and other hybrid structures [50] (Fig. 6).…”