Growth of crystalline ZnO nanostructures using pulsed laser deposition

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. (000ℓ)-oriented, hexagonal nanodots, typically 250 nm wide, were obtained on a-sapphire substrates. (112̄0)-oriented, aggregated nanostructures with a typical size of 300 nm were produced on r-sapphire substrates with an irregular distribution on the surface. (000ℓ)-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.