ZnO nanocrystals have been widely studied in optoelectronic and electronic fields such as UV-LEDs and UV detectors because of their unique optoelectronic properties. However, it is very difficult to fabricate high-quality p-type ZnO, so that a heterojunction structure of ZnO/p-type materials has attracted much attention as the device applications. Recently, diamond is attracting attention in combination with ZnO for photodetectors operated in the UV region because of its 5.47 eV band gap, highest thermal conductivity, high radiation resistance and good temperature stability. In this study, we synthesized ZnO nanowires on a diamond single crystal substrate by nanoparticle-assisted pulsed laser deposition (NAPLD), and investigated the structural and optical characteristics of the ZnO nanowires.

In the experiment, a sintered source target of ZnO was used. (001) single crystalline diamond substrate was put on a SiC heater in a vacuum chamber and the ZnO target located against the substrate was ablated with the third harmonics of a Q-switched Nd:YAG laser at 355 nm. In the condition of 27-kPa-Ar atmosphere and a laser fluence of 1 J/cm² with a substrate temperature of 750 ºC for 20 min, vertically aligned ZnO nanowires were grown on the diamond. The diameter and length of the nanowires were about 100 nm and 1.5 μm from SEM image, respectively. The nanowires have wurtzite crystalline structure oriented in the c-axis direction, which was confirmed by X-ray diffraction measurement. Photoluminescence measurements under He-Cd laser (325 nm) excitation show an UV emission centered at around 379 nm, which is the contribution of the near band edge emission of the wide band-gap ZnO, and weak broad visible emission attributed to the deep-level defects inside ZnO lattices. The results indicate a low concentration of deep-level defects inside ZnO lattices.