Due to its wide direct band gap and large exciton binding energy allowing for efficient excitonic emission at room
temperature, ZnO has attracted attention as a luminescent material in various applications such as UV-light emitting
diodes, chemical sensors and solar cells. While low-cost growth techniques, such as chemical bath deposition
(CBD), of ZnO thin films and nanostructures have been already reported; nevertheless, ZnO thin films and
nanostructures grown by costly techniques, such as metalorganic vapour phase epitaxy, still present the most
interesting properties in terms of crystallinity and internal quantum efficiency.
In this work, we report on highly efficient and highly crystalline ZnO micropods grown by CBD at a low
temperature (< 90°C). XRD and low-temperature photoluminescence (PL) investigations on as-grown ZnO
micropods revealed a highly crystalline ZnO structure and a strong UV excitonic emission with internal quantum
efficiency (IQE) of 10% at room temperature. Thermal annealing at 900°C of the as-grown ZnO micropods leads to
further enhancement in their structural and optical properties. Low-temperature PL measurements on annealed ZnO
micropods showed the presence of phonon replicas, which was not the case for as-grown samples. The appearance
of phonon replicas provides a strong proof of the improved crystal quality of annealed ZnO micropods. Most
importantly, low-temperature PL reveals an improved IQE of 15% in the excitonic emission of ZnO micropods. The
ZnO micropods IQE reported here are comparable to IQEs reported on ZnO structures obtained by costly and more
complex growth techniques. These results are of great interest demonstrating that high quality ZnO microstructures
can be obtained at low temperatures using a low-cost CBD growth technique.
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