Growth of crystalline ZnO nanostructures using pulsed laser deposition

Abstract

Pulsed laser deposition was used to grow epitaxial ZnO nanocrystalline structures on a -, c - and r -plane sapphire substrates, respectively. All of the growths were carried out at the same substrate temperature of ∼700 ∘C in 10 Pa of oxygen without any added inert gases. Atomic force microscopy, scanning electron microscopy, x-ray diffraction and photoluminescence were used to characterize the samples. ( 000 ℓ ) -oriented, hexagonal nanodots, typically 250 nm wide, were obtained on a -sapphire substrates. ( 11 2 ̄ 0 ) -oriented, aggregated nanostructures with a typical size of 300 nm were produced on r -sapphire substrates with an irregular distribution on the surface. ( 000 ℓ ) -oriented, nanoparticle-like structures with a typical size of 100 nm, were produced on the c -sapphire surface. The room-temperature photoluminescence of the ZnO nanostructured thin films grown on a - and c -sapphire were dominated by a broad blue band emission centered at 2.85 eV photon energy. An intense free-exciton peak at 3.2436 eV photon energy with a width of 91 meV and a defect-related green band were the main features for the room-temperature photoluminescence of the ZnO nanostructured thin films grown on r -sapphire substrates. The high optical quality of the ZnO / r -sapphire material was confirmed by the presence of, or the narrow widths of, characteristic excitonic emission features in the corresponding low-temperature photoluminescence spectrum.