Abstract
Ultraviolet (UV) sensitive devices based on spin-coated zinc-oxide nanoparticles (ZnO) were fabricated and characterised. They were subsequently stored in the ambient and dark conditions with low humidity for 56 days, during which time they were intermittently recharacterised to determine the aging effect on their sensing properties, including responsivity, sensitivity, and response and recovery times. Over the 56-day period, both the dark and illumination currents increased, causing the non-monotonic evolution of the performances of the devices – the responsivity improved by 9–18 folds, the sensitivity remained stable, and the response and recovery times deteriorated as they were 46 and 33 times longer, respectively. These changes were associated with an increase in the number of adsorbed oxygen molecules on the ZnO surface with time. This resulted in more photodesorbed oxygen molecules and thus more remaining charge carriers under illumination, which increased the photo-generated current and consequently responsivity. However, it also caused the current to rise and decay more slowly when the illumination appeared and disappeared, respectively, leading to the prolonged response and recovery times. The longer recovery times led in an increase in dark current, which, when combined with an increase in illumination current, resulted in a stable sensitivity. The trends of these sensing parameters were similar, but to varying degrees, regardless of the change in the radiation levels and ZnO layer thicknesses.
Published Version
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