Synthesis and optical properties of well aligned ZnO nanorods on GaN by hydrothermal synthesis

Uniformly distributed ZnO nanorods with diameter 80-120 nm and length 2 mu m have been grown at low temperatures on GaN by a catalyst-free and inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. XRD and TEM studies show that the ZnO nanorods are single crystals and are well oriented along the c-axis of the crystal plane. The room-temperature photoluminescence measurements have shown a dominant ultraviolet peak at 3.23 eV with high intensity, which are comparable to those found in high-quality ZnO films. Through the photoluminescence measurement at a low temperature, the ZnO nanorods show a strong near band edge emission with weak deep level emission and also a free-to-bound transition with its phonon replicas. The temperature dependence of these excitonic emission and multiple phonon replicas from 4 to 250 K have been observed and their origins have been identified.