Investigation of Optical Properties and Defects Structure of Rare Earth (Sm, Gd, Ho) Doped Zinc Oxide Thin Films Prepared by Pulsed Laser Deposition

Rare earths (RE = Sm, Gd, Ho) doped ZnO thin films were grown by pulsed laser deposition in oxygen ambient at pressure of 10 Pa on fused silica and Si(100) substrates at room temperature. A good optical quality of the films was confirmed by transmittance measurement in the visible spectral region. Photoluminescence suggested RE3+ oxidation state as confirmed at ZnO:Sm, where local structure was inhomogeneous. ZnO:Sm film exhibited the highest electrical resistivity while ZnO:Ho the lowest. Nanocrystalline structure of the films was observed by atomic force microscopy and X-ray diffraction. Defects structure was examined by variable energy positron annihilation spectroscopy. All ZnO:RE films exhibited significantly higher values of the S parameter as well as shorter positron diffusion lengths compared to ZnO monocrystal reference due to trapping of positrons at open volumes associated with grain boundaries. We observed the impact of the type of RE dopant on optical and electrotransport properties while the defect structure remained unchanged.