Effect of consumption of the sol–gel deposited ZnO seed layer on the growth and properties of high quality ZnO nanorods

Abstract

Zinc oxide (ZnO) nanorods (NRs) with high transmittance and low resistance were produced on glass substrates in two steps. Initially, a ZnO seed layer was produced via sol–gel spin coating and heat treatment, and in the second step ZnO-NRs were grown on the ZnO seed layer via hydrothermal growth. The ZnO samples were identified by XRD. Average crystallite sizes were found to be 45 and 60 nm, for the ZnO seed layer and the ZnO-NRs, respectively, from XRD results using the Scherrer formula. Average grain sizes of the ZnO thin films were determined with FE-SEM and found to be 62 and 68 nm for the ZnO seed layer and the ZnO-NRs, respectively. The ZnO-NRs were very dense when grown to a (film) thickness exceeding that of the seed layer. After the growth of the ZnO-NRs, the starting thickness of ZnO seed layer was reduced from 360 to 60 nm. This revealed that the ZnO-NRs’ growth consumes the sol–gel deposited ZnO seed layer significantly, which in turn affects the NR array’s properties. The electrical conductivity values of the ZnO seed layer and ZnO-NRs/ZnO seed structure films were measured as 6.98 × 10⁻⁹ and 2.08 × 10⁻⁸ Ω⁻¹ cm⁻¹ at 25 °C, and 9.31 × 10⁻⁸ and 8.99 × 10⁻⁷ Ω⁻¹ cm⁻¹ at 300 °C, respectively. In other words, the ZnO-NRs/ZnO seed structure had higher electrical conductivity than the starting ZnO seed layer alone. In agreement, the ZnO-NRs/ZnO seed structure had a much higher transmittance (80–90% in the UV–Vis range) than the starting seed layer. These suggested that the ZnO-NRs has better crystal quality with lower defects along their length and hence the seed layer consumption is a benefical factor in obtaining ZnO NR arrays with high quality.