Local Strucure,transport And Magnetic Properties Of Co-doped In₂O₃ Diluted Magnetic Semiconductors

In this paper, the Fe/Sn, Fe/Mg and Mn/Mg co-doped In2O3 diluted magnetic semiconductors(DMS) films were deposited on Si O2/Si(100) and super white glass substrates by RF-magnetron sputtering technique.The structure and physical properties of In2O3 DMS films have been investigated systemically by XRD, XPS, SQUID, Hall, R-T, MR and U-V et al., the result are following:1. The Fe/Sn co-doped In2O3 films have a Cubic Bixbyite structure, no traces of Fe, Sn metal cluster and related oxide secondary phases were observed for all the films. Fe presents mixed valence state of +2 and +3 and Sn presents as +4 valence state from the XPS results. The detailed XANES analyses and full multiple-scattering ab initio calculations indicate that the doped Fe ions substitute for In3+ sites of In2O3 lattice and form FeIn2+ + VO complex with the two O vacancies in the nearest coordination shell. The transport properties measurements show that all the films show semiconducting behavior, and carrier concentration decreases and the resistivity increase with the increase of the Fe concentration. The electronic conducting mechanism is dominated by Mott variable range hopping(VRH) behavior at low temperature and Hard bandgap hopping behavior at high temperature, suggesting that the carriers are strongly localized. The magnetoresistance(MR) measurements indicate that the low Fe-doped films with high carrier concentration only show a negative MR component at different temperatures, whereas high Fe doped films with low carrier concentration show the positive MR component at high field at 10 K. As temperature increased to above 15 K, the negative MR behavior again dominates for the high Fe doped films. All the films show intrinsic room-tempertrrature(RT) ferromagnetism, and Ms decreases with Fe doping. The observed intrinsic RT ferromagnetism can be asscibed to the strong lattice distortion and electrons bound in defect states associated with oxygen vacancies.2. The deposited Fe/Mg co-doped In2O3 films have a cubic bixbyite structure and no traces of Fe metal cluster and related oxide secondary phases were observed in films. The doped Fe atoms exists in the ionic form with the mixed divalent state of Fe2+ and Fe3+, and substitute for In1 sites of In2O3 lattice with the two O vacancies in the nearest coordination shell. The film with Fe concentration x=0.02 shows a crossover from semiconducting to metallic transport behavior at 191 K. With further increasing Fe concentration, the films display good semiconducting behavior. Hall measurements show that the carrier concentration decreases and the resistivity increase with the increase of the Fe concentration. The conductive mechanism at low temperature, Mott variable range hopping dominant, and Hard bandgap hopping dominant at high tenperature. In low Fe doping concentration, films show negative magnetic resistance. Films show positive magnetic resistance at low temperrature withing the Fe doping concentratin. For films with high Fe doping concentration, magnetic resistance from positive towards negative withing the increase of temperature. the thin film magnetic resistance from negative towards positive magnetic resistance withing Fe doping concentration increases; and when Fe doping concentration is higher, the magnetic resistance to positive magnetoresistance, until vanishing with the increase of temperature. The existence of the magnetic resistance, positive and negative forms are under the influence of doping elements concentration, temperature. The transmittance intensity of films and the band gap desreases with the increases of Fe concentration. All films have intrinsic room-tempertrrature ferromagnetism, and Ms increases then decreases with Fe increases concentration. The strong lattice distortion and oxygen vacancies around Fe ion space is intrinsic room-temperature ferromagnetism of the important reasons.3. The deposited Mn/Mg co-doped In2O3 films have a cubic bixbyite structure, and no traces of Mn metal cluster and related oxide secondary phases were obser ved in films. The doped Mn element presents +2 valence state and substitute for In1 sites of In2O3 lattice. The doped Mn ions form MnIn2+ + VO complex with the one O vacancy in the nearest coordination shell. The films show semiconducting behavior, and carrier concentration decreases and the resistivity increase with the increase of the Mn concentration, and the conduction mechanism of the Mott variable range hopping and Hard bandgap hopping. The transmittance intensity of films and the band gap desreases with the increases of Fe concentration, resulting in an obvious red shift in the absorption edge position. All the films show intrinsic RT ferromagnetism, and Ms decreases increases with increasing Mn concentration. The strong lattice distortion and oxygen vacancies around Fe ion space is intrinsic room-temperature ferromagnetism of the important reasons.