Comparative studies on the growth behavior of ZnO nanorods by metalorganic chemical vapor deposition depending on the type of substrates

The growth behavior of ZnO nanorods on various substrates including Si (1 1 1), Si (0 0 1), Al2O3 (0 0 0 1), GaN/Al2O3 (0 0 0 1) and ZnO (0 0 0 1) by metalorganic chemical vapor deposition without using any catalyst was investigated in a comparative way. The alignment of ZnO nanorods greatly depends on the substrates used for the growth. The ZnO nanorods grown on Si (1 1 1) and Si (0 0 1) are vertically aligned but randomly oriented in the in-plane direction. The vertically aligned ZnO nanorods grown on Al2O3 (0 0 0 1) show an in-plane alignment with a broad mosaic distribution of ∼9°. In contrast, epitaxially aligned ZnO nanorods with an extremely narrow in-plane and out-of-plane mosaic distribution grow on the lattice-matched substrates such as GaN/Al2O3 (0 0 0 1) and ZnO (0 0 0 1) without showing a continuous interfacial ZnO layer observed in the samples grown on Si (1 1 1), Si (0 0 1) and Al2O3 (0 0 0 1). Differently from the alignment nature, all the ZnO nanorods exhibit only high band edge emission peaks with no noticeable deep level emissions in the low-temperature photoluminescence measurements, supporting that the crystalline and optical quality of an individual ZnO nanorod is basically similar irrespective of the type of the substrates used.