Zinc oxide (ZnO) thin films are promising materials for sensing and detecting UV and for developing flexible wearable electronics and more, making them particularly suitable for IoT (Internet of Things) applications due to their optical and electrical tunability via size, shape, and surface morphology modulation. However, limited understanding of ZnO nanostructure behaviours, notably its growth dynamics related to defects and surface morphologies and carrier transport have confined their broader applications. In this manuscript, we report an optimum ZnO grain size which produces high photo-response on a UV photodetector, fabricated on quartz substrate using chemical and thermal annealing methods. Three different ZnO nanostructure films, namely, ZnO-1, ZnO-2 and ZnO-3 with different grain sizes (∼20 ± 2 nm, ∼41 ± 4 nm and ∼61 ± 7 nm) and surface morphologies, were synthesized at different annealing temperatures. Optical analysis using UV–visible spectra showed that the band gaps for ZnO-1, ZnO-2 and ZnO-3 were ∼3.29, ∼3.22 and ∼3.13 eV, respectively. The photoluminescence spectra showed that the UV emission and visible broad band emission correspond to the band edge and defect levels of ZnO. Furthermore, the electrical characterization using three terminal devices showed an enhanced transconductance from ∼3.22 × 10 −9 S to ∼2.0 × 10 −6 S with increasing grain size of ZnO nanostructure films. An optimal photo-response of 100 A/W at 10 V was achieved by balancing light absorption and carrier collection efficiency for the ZnO film with a grain size of ∼41 ± 4. In conclusion, the high-performance ZnO films that we developed here bear high promise in optoelectronic, UV detection, and other sensing applications.
Ghimire et al. (2026) studied this question.