Lamb Wave Resonator for UV Photodetection and Impact of Induced Piezopotential on Schottky Barrier Height Toward Enhanced Sensitivity

In this work, a Lamb wave resonator-based UV photodetector is fabricated using ZnO thin film grown on SiO2/Si membrane. Electrical studies of the fabricated ZnO/SiO2/Si Lamb wave resonator device reveals a change in current ( ${I}_{\text {on}}/{I}_{\text {off}} \sim 10^{{4}}{)}$ upon UV illumination ( $\lambda =365$ nm, Intensity = 0.2 mW/cm $^{{2}}{)}$ with a responsivity (56.34 A/W), detectivity ( ${6}.{5}\times {10} ^{{12}}$ Jones) and response and recovery time of 280 and 25 ms, respectively. Frequency response of the fabricated Lamb wave device demonstrates the presence of multiple modes corresponding to symmetric and anti-symmetric modes and their higher harmonics. It is observed that the highest mode ( ${A}_{{2}}{)}$ of Lamb wave resonator (192.27 MHz) shows maximum frequency shift (535 kHz(mW/cm $^{{2}}{)}^{-{1}}{)}$ and very high sensitivity of $2.78\times 10^{{3}}$ ppm(mW/cm $^{{2}}{)}^{-{1}}$ . In addition, various mechanism involved in the photodetection are being discussed. Especially, the effect of induced piezo-potential on Schottky barrier height (SBH) in the acoustic device and corresponding enhancement in the photodetector performance is discussed. It is observed that Lamb wave device with Schottky contact type IDTs shows higher UV detection performance as compared to the that with Ohmic type IDTs contact. This effect can be explained using effect of induced piezo-potential on SBH while the acoustic wave is propagating in the piezoelectric substrate of the surface acoustic wave (SAW) devices. Thus, the study demonstrates the high potential of indigenously developed Lamb wave resonator-based UV photodetector (ZnO/SiO2/Si) for civil and military field applications.