Local structural properties and growth mechanism of ZnO nanorods grown on various substrates

Abstract

We present the systematic study of the growth mechanism of ZnO nanorods grown on Al2O3 substrates with ZnO homo-buffer, n-GaN and p-GaN interlayers. Vertically aligned ZnO nanorods with diameter of 50 nm and lengths of range of 0.1 - 2 μm were synthesized at the substrate temperature of 350 - 500 °C by catalyst-free metal-organic chemical vapor deposition. A thin ZnO film was observed underneath the ZnO nanorods grown on Al 2O3, ZnO homo-buffer layers and p-GaN interlayers and the film thickness varied from 0.1 μm to 0.55 μm depending on the substrates while the film was negligible on an n-GaN interlayer. The residual strain of the ZnO nanorods grown on Al2O3 substrates was reduced to less than one fifth of the original value by employing a n-GaN interlayer. The n-GaN interlayer also enhanced the orientations among the nanorods in the ab-plane. The extended x-ray absorption fine structure measurements revealed that there were a substantial amount of disorders in the bonding lengths of the Zn-O pairs in the beginning of the ZnO nanorod growth on the Al 2O3 substrates with and without the n-GaN interlayer. The disorders of the Zn-O pairs located near the ab-plane were decreased as the nanorod length was increased above 0.1 μm implying that the strain relaxation of the ZnO crystals in the ab-plane was critical in the formation of ZnO nanorods. © 2007 IEEE.