Low temperature annealing effect on photoresponse of the bilayer structures of ZnO nanorod/nanodiamond films based on ultraviolet photodetector

• Improved photoresponse of ZnO nanorod (NR)/nanodiamond film (NDF) UV photodetector by annealing.
• Reduced non-diamond components in NDF layer results in a low dark current.
• Numerous Zn interstitial defects in ZnO NRs disrupted the carrier's trapping process.

This study presents a low temperature annealing process to improve the photoresponse of the ZnO nanorod (ZnO NR)/nanodiamond film (NDF)/glass substrate bilayer structure of an ultraviolet (UV) photodetector. The wurtzite structure of ZnO NRs with a diameter/length of 160 nm/2.7 μm was grown by the hydrothermal method on a 700-nm-thick NDF layer synthesized by a microwave plasma chemical vapor deposition system. A photoluminescence spectra showing a near-band-edge emission at 3.28 eV with a shoulder peak at 3.20 eV for the Zn interstitial was observed for the 200 °C annealed sample. The Raman spectra of samples showed an improved 1332 cm− 1 sp3 diamond quality and reduced the non-diamond components while increasing the annealing temperature. A high photoresponse of 249.6 can be achieved by a 150 °C annealing process, which is about 6 times better than the as-grown sample. The low dark current of 1.76 × 10− 5 A for the 150 °C annealing sample was believed to be due to the improvement of the interface quality between the NDF and ZnO layer. However, the Zn interstitial generated in the 200 °C annealed sample disrupted the carrier's trapping process, resulting in a lower photocurrent. In addition, this type of defect also caused the interface quality of the ZnO NR/NDF bilayer structure to degrade and increase the dark current. The experimental results indicated that the annealing temperature plays an important role in improving the photoresponse of ZnO NR/NDF bilayer structured UV photodetector.