The structural, electrical, and optical properties of layer-by-layer ZnO nanoparticles deposited using sol-gel spincoating technique were studied and now presented. Thicknesses of the thin films were varied by increasing thenumber of deposited layers. As part of our characterization process, XRD and FE-SEM were used to characterizethe structural properties, current-voltage measurements for the electrical properties, and UV-Vis spectra andphotoluminescence spectra for the optical properties of the ZnO thin films. ZnO thin films with thicknesses rangingfrom 14.2 nm to 62.7 nm were used in this work. Film with thickness of 42.7 nm gave the lowest resistivity among all,1.39×10-2 Ω·cm. Photoluminescence spectra showed two peaks which were in the UV emission centered at 380 nm,and visible emission centered at 590 nm. Optical transmittance spectra of the samples indicated that all films weretransparent (>88%) in the visible-NIR range. The optical band gap energy was estimated to be 3.21~3.26 eV, with bandgap increased with the thin film thickness

We have fabricated metal-semiconductor-metal- (MSM-) type ultraviolet (UV) photoconductive sensors using aluminium- (Al-) doped zinc oxide (ZnO) nanorod arrays that were annealed in different environments: air, oxygen, or a vacuum. The Al-doped ZnO nanorods had an average diameter of 60 nm with a thickness of approximately 600 nm that included the seed layer (with thickness~200 nm). Our results show that the vacuum-annealed nanorod-array-based UV photoconductive sensor has the highest photocurrent value of  2.43  ×  10-4 A. The high photocurrent is due to the high concentration of zinc (Zn) interstitials in the vacuum-annealed nanorod arrays. In contrast, the oxygen-annealing process applied to the Al-doped ZnO nanorod arrays produced highly sensitive UV photoconductive sensors, in which the sensitivity reached 55.6, due to the surface properties of the oxygen-annealed nanorods, which have a higher affinity for oxygen adsorption than the other samples and were thereby capable of reducing the sensor’s dark current. In addition, the sensor fabricated using the oxygen-annealed nanorod arrays had the lowest rise and decay time constants. Our result shows that the annealing environment greatly affects the surface condition and properties of the Al-doped ZnO nanorod arrays, which influences the performance of the UV photoconductive sensors.

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