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To enhance the field emission (FE) properties of emitters based on ZnO nanostructures, the growth of ZnO nanostructures on ZnO nanorods (NRs) (1–1.2 μm in length and ∼200 nm in diameter) in a disturbed hydrothermal growth (HTG) solution is demonstrated. Experimental results reveal that the degree of disturbance of the aqueous solution determines both the shape and location of the synthesized ZnO nanostructures. For stirring speeds of 300 and 600 rpm (rpm), NR-like ZnO nanostructures with a reduced uniform diameter (70–120 nm) and a tapered shape but a rough surface are grown on the basal plane of ZnO NRs, respectively. For stirring speeds of 900 and 1150 rpm, ZnO needles (40–70 nm and 15–20 nm in diameter, respectively) were synthesized along the {101̅0} planes of the ZnO NRs with coherent c-planes. FE characteristics of ZnO-NRs emitters with and without the second stage growth of ZnO nanostructures are reported and compared. Possible growth mechanisms which govern the physical characteristics of the ZnO nanostructures synthesized in the HTG process are proposed and discussed.

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A new two-step hydrothermal growth (HTG) process with a shorter processing time and better growth control is proposed for the synthesis of ZnO nanotapers (NTs). The application of HTG ZnO NTs as surface roughening nanostructures to improve the light output power (L op) of GaN-based LEDs is demonstrated. Compared with that of ZnO nanowires, the use of ZnO NTs leads to an improvement in L op by 24.5% at 350 mA, which could be attributed to the fact that tapered ends of ZnO NTs offer more constructive photon scattering to maximize light extraction.

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