Concurrent Improvement of Photocarrier Separation and Extraction in ZnO Nanocrystal Ultraviolet Photodetectors

Polycrystalline film photodetectors often suffer from several drawbacks, such as uncontrollable defect species, grain boundary scattering, and surface oxygen trapping/detrapping, hindering their practical applications in high-performance UV photodetection. In this work, we induce an acceptor-type zinc vacancy (V-Zn ) defect in zero-dimensional ZnO nanocrystals by a dual thermal annealing process, which has been closely examined by a defect-sensitive electron paramagnetic resonance technique. The optimization of annealing parameters can well tune the V-Zn concentration and induce a considerable self-powered behavior, which is believed to result from ionized acceptor enhanced charge separation. On the other aspect, the capping of metallic Zn can lead to the formation of abundant interface conducting channels for the highly efficient charge transport and extraction. The optimized responsivity is enhanced from 5.3 x 10(-3) to 15.3 A W-1, and the average rise and decay times remain at 36.6 and 101.8 ms, respectively. Conductive atomic force microscopy confirms a uniform photocurrent distribution in the annealed polycrystalline films, suggesting the significance of synergies of lattice defects and grain boundary conductive channels. This study unambiguously demonstrates a new route to engineer the photodetection in nanocrystalline oxides, providing a promising prospect for future low-cost, low-power-consumption micro-/nano-optoelectronic devices.