Effect of the seed layer on the UV photodetection properties of ZnO nanorods

Abstract

The ZnO seed layer, acting as nucleation center for the growth of ZnO nanorods (NRs), has strong impact on the optical and photodetection properties of ZnO-based UV photodetectors (PDs). In this paper, vertically aligned ZnO NRs were grown by varying the thickness of the seed layer in the range 50–125 nm, to investigate its influence on the recovery time of the PD. Single crystalline ZnO NRs were obtained as indicated by combined electron microscopy and X-ray diffraction analysis. The photoluminescence (PL) spectra proved that the lowest PL intensity (i.e.: the lowest recombination) belongs to the sample with seed layer thickness of 100 nm (labeled as NR-7). The carrier concentration of ZnO NR films was estimated from the slope of the Mott–Schottky plot. It was 1.49 × 10+20 cm−3 for seed layer thickness of 65 nm (NR-5), which was dramatically reduced to 5.44 × 10+17 cm−3 in the sample NR-9 (seed layer thickness 125 nm). Furthermore, the current-voltage (I-V) and chronoamperometric (I-t) analysis indicate a high UV responsivity under a UV irradiation. The fastest recovery time (0.1 s time decay constant) occurs in sample NR-7 (seed layer 100 nm thick). These results indicate that effective control of the electronic and optical properties in ZnO NRs can be obtained by proper tuning of the seed layer, enabling a simple and straightforward strategy to optimize NR functionality, depending on their planned use.