Enhancing ZnO film morphologies and properties via multilayered seed design for UV photodetection applications

The structural, morphological, optical, and electrical properties of ZnO nanorods (NRs) as a function of the number of ZnO seed layers (SLs) are investigated for ultraviolet photodetector (UV-PD) applications. SLs with one to seven cycles (SL1 to SL7) were deposited via a cost-effective sol-gel spin-coating technique on ITO substrates, followed by ZnO NR growth using a chemical bath deposition (CBD) approach, and the device electrodes were fabricated using the silver (Ag) paste technique. Characterization revealed that increasing the number of seed-layer cycles increased surface roughness and improved crystallinity, thereby directly influencing NR morphology. While NR density varied, all samples exhibited vertically aligned growth. The changes in structural and optical parameters, such as crystallite size, strain, stress, dislocation density, and optical bandgap, for each SL cycle count were examined. The highest crystallite size and lowest dislocation density were obtained for the ZnO NR sample with a 7-cycle (SL7), as 63.93 nm, and \(\:2.45\:\times\:{10}^{-4}\:{nm}^{-2}\) , respectively, which signifies superior crystallinity. Optical band gaps ranged from 3.87 to 4.14 eV, with ZnO NR7 having a 3.89 eV bandgap. Electrical characterization under 365 nm illumination demonstrated that the SL7 seed-layer sample exhibited superior photocurrent and photodetection performance. The ZnO NR7 sample achieved the highest responsivity ( \(\:2.53\:\times\:{10}^{-4}\) A/W) and detectivity ( \(\:7.97\:\times\:{10}^{8}\) Jones). The results show that the number of SL cycle count significantly affects the crystal quality, orientation, and optical bandgap of the growing ZnO NRs, and conclusively establish that engineering multilayer SLs is a critical and effective strategy for optimizing morphology and enhancing the optoelectronic performance of solution-processed ZnO NR-based UV sensors. Thanks to the concept of multilayered SL design for growing quality ZnO NRs, thereby improving the UV PD performance of the low-temperature Ag paste/ZnO NR device. This is the first report of this phenomenon. Overall, this study highlights the potential of ZnO NRs for nanophotonic sensors, offering a simple, cost-effective method for optimizing UV PDs.