Anisotropy of physical properties in pulsed laser-deposited ZnO films

In this paper, we report on the angular distribution of thickness, composition, microstructure and sheet resistance of a zinc oxide film obtained by pulsed laser deposition (PLD) at room temperature under 10(-6) mbar on a 40 mm large SiO2/Si substrate. Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electrical resistivity measurements were carried out to fully characterize the zinc oxide film for different zones of the substrate. The results show the anisotropy of its structural and physical properties along the substrate. In the external part of the film, which corresponds to an angular deviation of around 25 degrees-30 degrees from the normal to the laser impact, a pure (002) textured and stoichiometric ZnO is evidenced. In contrast, the formation of a nanocomposite is observed in its central part and exhibits nearly stoichiometric ZnO, oxygen-deficient ZnO1-x and metallic Zn nanocrystallites. Due to their small sizes (a few nm), such Zn nanocrystallites are not detected by classical theta/2 theta XRD and can only be evidenced by TEM experiments. The non-uniformities in composition, microstructure and physical properties of the films are due to the PLD process for which the angular distribution of the Zn and O species in the ablation plume is not homogeneous. The observed anisotropy is not detrimental for PLD experiments performed with low size substrate (1-2 cm(2)) which is located in the main propagation axis of the PLD plume.

Automated summary

This paper reports on the angular distribution of various properties of a zinc oxide film obtained by pulsed laser deposition on a large SiO2/Si substrate. The film exhibits anisotropy in its structural and physical properties along the substrate. The composition and microstructure of the film also varies in different regions of the substrate.