Nanoparticle-Composed Photosensitive Thin Films Based on ZnO

In this work, atmospheric pulsed laser deposition was used to prepare photosensitive elements. This technology is a practical and relatively inexpensive way of obtaining highly porous nanostructures composed of nanoparticles or nanoaggregates characterized by a large surface-to-volume ratio. Samples were produced via laser nanosecond or picosecond laser ablation of pure ZnO or mixed ZnO-TiO₂ targets on quartz substrates with pre-deposited gold electrodes. The structure, morphology, optical, and electrical properties of the nanostructures obtained were studied regarding the sample composition and laser ablation regime applied. The ablation of a mixed ZnO-TiO₂ target led to the fabrication of composite samples consisting of ZnO and Zn₂TiO₄ nanoparticles. The electrical properties of pure and composite samples were studied under exposure to UV light irradiation. It was found that the photosensitive properties of the samples depended on the ablation regime applied. The dark current measured for the nanosecond-deposited samples was a few nA, which was an order of magnitude larger compared to the picosecond-deposited samples. The value of the photogenerated current of the nanosecond-deposited samples was 10³-times higher than that of the picosecond-deposited samples. This is due to the lower absorption of the picosecond-deposited samples, as well as to the presence of defect-related radiative recombination in the picosecond-deposited samples, which limits the photocurrent rise. The estimated rise and decay times were longer for the composite samples independently of the deposition regime applied.