Laser annealing effects on the structural, optical and magnetic properties of sputtered Zn0.95Co0.05O thin film

We have used reactive magnetron co-sputtering to grow Zn0.95Co0.05O dilute magnetic semiconductor (DMS) on 400 nm thick of (0 0 0 1) Al2O3 substrate at 600 °C. After deposition the films were irradiated by ArF excimer laser (λ = 193 nm, τ = 20 ns) source, with energy density equal to 0.4 J/cm2 for two shoots. The effects of laser annealing on structural, optical and magnetic properties of Zn095Co0.05O thin films on Al2O3 substrate were investigated using X-ray diffraction (XRD), IR absorption spectra, Raman spectroscopy, atomic force microscopy (AFM) and SQUID magnetometry. XRD analysis showed that the annealed film is textured with c-axis of the wurtzite structure along the growth direction. The IR absorption spectra of the sample showed three absorptions peaks before and after laser annealing due to the transitions between the crystal-field-split 3d levels of tetrahedral Co2+ substituting Zn2+ ions. Raman spectra showed the appearance of an additional mode which is an indicator for incorporation of Co2+ ions into the ZnO matrix. The roughness Rms value of the film evaluated by AFM decreased after laser annealing indicates a good surface topography. Room temperature magnetization measurements performed by SQUID magnetometry showed the presence of ferromagnetism with a saturation magnetization increased after ArF excimer laser annealing.