Structural properties of ZnO films grown by picosecond pulsed-laser deposition

Zinc oxide thin films have been grown on c-cut (0 0 0 1) and r-cut (image) sapphire substrates by pulsed-laser deposition using a Nd:YAG laser operating at 355 nm in picosecond regime (pulse duration: 42 ps). The composition and the structural properties of the films have been investigated by scanning electron microscopy, Rutherford backscattering spectroscopy and X-ray diffraction according to different substrate temperatures. The RBS spectra show a Zn/O ratio close to 1.1 with a constant in-depth oxygen concentration. The XRD diagrams in Bragg–Brentano geometry display a preferred orientation depending on the used substrate. The large width of XRD peaks is indicative of a small coherence length. In addition, according to the pole figures recorded in asymmetric configuration, epitaxial relationships between substrate and film are evidenced. An increase in the substrate temperature leads to a film crystalline quality improvement. The results are discussed regarding the well-known properties of ZnO films obtained by nanosecond and femtosecond PLD.