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UBC Theses and Dissertations

UV-LED photo-activated metal oxide semiconductors for gas sensing application : fabrication and performance evaluation Espid, Ehsan


The idea of functionalizing chemical gas sensors at room temperature as well as making them smaller and more efficient has initiated important progresses in the last few years among scientists worldwide. Ultraviolet Light Emitting Diode (UV-LED) technology has shown its capability to fulfill the gap between laboratorial and industrial production of room temperature gas sensors. In this research, a review on the performances, preparation techniques, and most influential factors of several photo-activated metal oxide semiconductor gas sensors under UV-LED irradiation was conducted. Further, a comparative study on the development of sensitive gas sensors using ZnO and In₂O₃ semiconductors for NO₂ gas detection was performed. The results indicated that the sensitivity of In₂O₃ to NO₂ is approximately two times greater than that of ZnO for all the experimented irradiances. The highest sensitivities with complete recovery for the ZnO and In₂O₃ based sensors were obtained at 1.2 mW/cm² and 2.8 mW/cm² irradiances, respectively. In general, the In₂O₃ sensors required a higher UV irradiance compared to ZnO sensors, to prevent permanent adsorption of target gas molecules on the surface. To further increase the sensitivity and reduce the response time, n-type semiconductor oxides of ZnO and In₂O₃ were coupled using co-precipitation method, to obtain nano-crystalline composite sensing materials. The composition, structure and optical properties of the prepared samples were characterized by EDS, XRD, SEM, XPS and UV-Vis analyses. The composite materials showed higher sensitivity towards NO₂ with a 200s decrease in response time compared to pristine samples. A favorable composition ratio of [In]:[Zn] was determined to be 1:2 for the nano-composite particles, with 2.21 sensitivity as the highest sensing performance to 5 ppm NO₂. The high sensitivity of this combination is attributed to the morphology and composite porous structure, as well as lower band-gap of the target composite. The irradiance of 1.7 mW/cm² provided the highest sensitivity, short response time and a complete recovery for the ZnO/In₂O₃ composite structures, within the experimented range. It’s believed that, ZnO favors the flow of charge carriers and increases the surface area, while In₂O₃ acts as active light absorption centers and enhances chemisorption ability in the composite.

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