Proton implantation effect on ZnO nanorod growth

We demonstrate the influences of charges near the substrate surfaces on vertically aligned ZnO nanorod growth. ZnO nanorods were fabricated on Al ₂O₃ substrates with and without GaN interlayers by catalyst-free metal-organic chemical vapor (MOCVD) deposition. It has been recognized that ZnO nanorods grown on an n-type GaN film had a uniform size and a high crystal quality, comparing to those of the nanorods on a p-type GaN interlayer. We intentionally implanted protons in the sapphire substrates and n-GaN interlayers and investigated the ZnO nanorod growth. The protons were implanted around 570 nm and 300 nm depth for the GaN interlayer and sapphire substrate, respectively. Field-emission transmission electron microscope measurements confirmed no surface damage by the proton treatment. The ZnO on the proton-treated GaN interlayer formed into nanorods with a low quality. As the ZnO was deposited on the proton-treated Al₂O₃, it became an amorphous film. These results implied that the charge greatly affected on the ZnO nanorod growth. The protons implanted in the n-GaN interlayer might be caught by the anions in the interlayer while in the sapphire, the positive charges could freely move. The positive charge near the surface might prevent Zn²⁺ atom bonding to the substrate. Our observation strongly suggested that direct and uniform bonding of zinc atoms to the substrate surface is critical in ZnO nanorod growth.