Structural, morphological, optical and magnetic properties of RF sputtered Co doped ZnO diluted magnetic semiconductor for spintronic applications

This article reports the fabrication and characterization of thin films of pure and cobalt doped ZnO (Co at 4% and 7%), a transparent diluted magnetic semiconductor (DMS) grown on 'Si' and glass substrates by RF magnetron sputtering technique. The crystalline structure and phase of the grown thin films were analyzed by using X-ray diffraction (XRD) method which confirmed the hexagonal wurtzite structure of the ZnO with slight lattice strain and change in orientation of the planes. The XRD also confirmed that, the films exhibit prominent peaks of (1 0 1) and (1 0 3) with polycrystalline nature. The morphology of the grown thin films was investigated by scanning electron microscopy (SEM) which confirmed the variation of micro-structure and size of the polycrystalline film's surface. The energy dispersive X-ray spectra (EDS) from SEM have confirmed the presence of constituent elements in the films and concentration (in %) of each element. The crystalline properties and morphology of the film's cross-section were studied by high resolution transmission electron microscopy (HR-TEM). The average thickness of the films was found to be about 600 nm from the cross-section electron microscopic images. The selected area electron diffraction (SAED) pattern from TEM was recorded for the Co (7%) doped ZnO film which has good polycrystalline quality. The optical transmittance of the films coated on corning glass substrates was investigated by UV-Visible spectrophotometer for pure, 4% and 7% Co doped ZnO films, which revealed the optical transparency of 85%, 75% and 65%, respectively. The room temperature ferromagnetism of the doped films was analysed by vibrating sample magnetometry and magneto optic Kerr effect. It was found that the ferromagnetic behaviour of films increases with 'Co' content and the results were discussed in detail.