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Abstract: Epitaxial ZnO thin films have been synthesized directly on Si(111) substrates by pulsed laser deposition (PLD) in vacuum. The reflection high-energy electron diffraction (RHEED) indicates that streaky patterns can be clearly observed from the ZnO epilayers prepared at 600 and 650°C, revealing a two-dimensional (2D) growth mode. While the ZnO thin film deposited in oxygen ambient shows ring RHEED pattern. There is a compressive in-plane stress existing in the ZnO epitaxial film, but a tensile one in the polycrystalline film. Compared with the ZnO epilayer, the ZnO polycrystalline film shows more intense ultraviolet emission (UVE) with a small full width at half maximum (FWHM) of 89meV. It is suggested that the atomically flat epilayers may be powerfully used as transitive stratums to grow high-quality ZnO films suitable for the fabrication of optoelectronic devices. [Copyright &y& Elsevier]

Abstract: ZnO thin films with highly c-axis orientation have been fabricated on p-type Si(111) substrates at 400°C by pulsed laser deposition (PLD) from a metallic Zn target with oxygen pressures between 0.1 and 0.7mbar. Experimental results indicate that the films deposited at 0.3 and 0.5mbar have better crystalline and optical quality and flatter surfaces than the films prepared at other pressures. The full width at half maximum (FWHM) of (0002) diffraction peak decreases remarkably from 0.46 to 0.19° with increasing annealing temperature for the film prepared at 0.3mbar. In photoluminescence (PL) spectra at room temperature, the annealed film at 700°C exhibits a smaller ultraviolet (UV) peak FWHM of 108meV than the as-grown film (119meV). However, an enhanced deep-level emission is observed. Possible origins to above results are discussed. [Copyright &y& Elsevier]

ZnO thin films were fabricated on Si (1 1 1) substrates by oxidation of metallic Zn films in air. A thin layer of Au was used to enhance the adhesion of the Zn atoms to the Si surface during depositing the Zn films on the substrates at room temperature (RT) by thermal evaporation. X-ray diffraction (XRD) studies indicate that the ZnO film prepared at 500 °C has better crystalline quality than films prepared at other temperatures. In photoluminescence (PL) spectra at room temperature, the film oxidized at 500 °C exhibits the biggest intensity ratio of 162 of ultraviolet (UV) emission to deep-level emission and the narrowest UV peak full width at half maximum (FWHM) of 94.8 meV. These results reveal that high-quality ZnO thin films with good crystallinity and strong UV emission can be achieved at such low temperature. It was also observed that the deep-level emission would become dominant in the PL spectra for the samples annealed at high temperatures above 700 °C, and the possible origin was discussed. [Copyright &y& Elsevier]