ZnO Nanorod-Based Ultraviolet Photodetector Prepared on Patterned Sapphire Substrates

A patterned sapphire substrate with a submicron hole array structure was used to fabricate ZnO nanorod (NR) array by low-temperature hydrothermal method. A ZnO seed layer was spin-coated using sol-gel process and then etched to form separated seed islands. Different concentrations of zinc acetate in the hydrothermal solution were performed for ZnO NR synthesis to investigate ultraviolet (UV) photo-response properties. The ZnO NRs synthesized on the patterned substrates were oriented at various inclined angles. The diameter of the NRs increased and their surface-to-volume ratio decreased as the concentrations of zinc acetate increased from 0.01 to 0.04 M. X-ray diffraction and photoluminescence analyses showed that the NRs synthesized at a higher zinc acetate concentration had better crystal quality and fewer defects. The current-voltage characteristics of the ZnO NR-based metal-semiconductor-metal photodetectors exhibited a linear relationship, suggesting an Ohmic contact between NRs and Al electrodes. The UV response, defined by the resistance ratio (Rdark/RUV), of the photodetectors increased with the decreasing zinc acetate concentration from 0.04 to 0.01 M. Compared to traditional vertically aligned NR array on plain substrates, the proposed ZnO NR-based photodetector on the patterned substrates achieved improved UV responses, and the average increment for samples of 0.01-0.04 M was 145%.