Oxygen Vacancies Engineering in Thick Semiconductor Films via Deep Ultraviolet Photoactivation for Selective and Sensitive Gas Sensing

Room-temperature detection of volatile organic compounds in particle-per-billion concentrations is critical for the development of wearable and distributed sensor networks. However, sensitivity and selectivity are limited at low operating temperatures. Here, a strategy is proposed to substantially improve the performance of semiconductor sensors. Tunable oxygen vacancies in thick 3D networks of metal oxide nanoparticles are engineered using deep ultraviolet photoactivation. High selectivity and sensitivity are achieved by optimizing the electronic structure and surface activity while preserving the 3D morphology. Cross-sectional depth analysis reveals oxygen vacancies present at various depths (approximate to 24% at a depth of 1.13 mu m), with a uniform distribution throughout the thick films. This results in approximate to 58% increase in the sensitivity of ZnO to 20-ppb ethanol at room temperature while approximate to 51% and 64% decrease in the response and recovery times, respectively. At an operating temperature of 150 degrees C, oxygen-vacant nanostructures achieve a lower limit of detection of 2 ppb. Density functional theory analysis shows that inducing oxygen vacancies reduces activation energy for ethanol adsorption and dissociation, leading to improved sensing performance. This scalable approach has the potential for designing low-power wearable chemical and bio-sensors and tuning the activity and band structure of porous, thick oxide films for multiple applications.