Hydrothermally grown defect-free ZnO nanorods with high angular distribution for enhanced excitonic emission

Abstract

Low-temperature hydrothermal growth has emerged as a popular method for the fabrication of ZnO nanorods (NRs), increasing the functionality and utility of ZnO-based devices. In this work, we study the influence of growth time, temperature and seed layer on the dimensions and angular distribution of hydrothermally grown ZnO NRs. High-quality ZnO NRs with a crisscrossed 60° angular distribution with respect to the substrate normal have been grown with a small diameter (20–60 nm) and a length of approximately 600 nm. We show that, within the ideal range of growth parameters (70–100°C for 2–4 hours), the growth time and temperature have no controllable influence on diameter and length, while the deposition method and size of the pre-growth deposited ZnO seeds affects diameter and NR angular alignment. Control over both is important for device structures involving wave-guided, angular dependent light emission and for high sensitivity and speed of chemical sensors. Furthermore, we demonstrate advantages of using crisscross-aligned ZnO NRs over planar ZnO for the enhancement of ZnO excitonic emission by optical coupling with gold nanoparticles (NPs). These results can be readily adapted for various applications that involve surface (NP) coating-mediated enhancement of both light emission or injection.