Ultrasensitive NO2 Gas Detection using ALD-Grown ZnO-SiO2/Si Thin Film-based UV Sensors

In this study, nitrogen dioxide (NO₂) gas sensors based on zinc oxide-silicon (ZnO–Si) and zinc oxide-silicon dioxide-silicon (ZnO–SiO₂–Si) configurations were fabricated to study their response to ultraviolet (UV) radiation at room temperature (300 K). Single and polycrystalline ZnO layers were deposited using atomic layer deposition (ALD) on silicon and silica substrates. The structure and composition of the films were studied using various characterization techniques. The current-voltage (I-V) characteristics of these sensors’ UV illumination (~365 nm) have been investigated. The gas sensing performance of both configurations was analyzed with and without the UV source for varied concentrations of NO₂ gas. Exposure to UV light significantly improved the recovery times of the sensors. Specifically, the recovery time for the Si-based sensor decreased from 1578 seconds to 24 seconds, while for the SiO₂-based sensor, it reduced from 540 seconds to 5 seconds. The response time of ZnO–Si was found to be 2 seconds and ZnO–SiO₂–Si to be 1 second. Under irradiation, the sensitivity factor increased from 8.29 × 10⁷ to 5.79 × 10^8% ppm^-1 for the ZnO–SiO₂–Si sensor. It reached a maximum value of 9.12 × 10¹¹% ppm^-1, which is extremely high compared to similar devices.