Abstract: Zinc oxide (ZnO) serves as a crucial functional semiconductor with a wide direct bandgap of approximately 3.37 eV. Solvothermal reaction is commonly used in the synthesis of ZnO micro/nanostructures, given its low cost, simplicity, and easy implementation. Moreover, ZnO morphology engineering has become desirable through the alteration of minor conditions in the reaction process, particularly at room temperature. In this work, ZnO micro/nanostructures were synthesized in a solution by varying the amounts of the ammonia added at low temperatures (including room temperature). The formation of Zn²⁺ complexes by ammonia in the precursor regulated the reaction rate of the morphology engineering of ZnO, which resulted in various structures, such as nanoparticles, nanosheets, microflowers, and single crystals. Finally, the obtained ZnO was used in the optoelectronic application of ultraviolet detectors.