Direct observation of thermally generated electron-hole pairs in ZnO nanorods with surface acoustic wave

Surface acoustic wave (SAW) sensors have been emerged as alluring candidates with myriads of applications in the realm of gas sensors, biosensors, and UV light detecting technology. In this study, SAW thermoelectric sensor, with the center frequency of ∼80 MHz, was fabricated by a vertical growth of ZnO nanorods on ST-X cut quartz substrate by dint of aqueous chemical growth method. The SAW device properties were estimated by glancing at the transmission spectrum characteristics like the shift in frequency and the decrease in signal amplitude. In the temperature range of 20 °C to 160 °C, frequency shift of ∼40 kHz, with ∼1 dB descent for each 20 °C period, was observed in the negative direction. Also, when the sensor was exposed to 365 nm UV light, an additional negative frequency shift of ∼11.6 kHz was realized for each 20 °C period. The frequency shift and the decrease in the signal amplitude were caused by an increment in the surface conductivity of SAW sensor because of thermal and photo-generated carriers.