Growth and ferromagnetic semiconducting properties of titanium dioxide thin films: An oxide-diluted magnetic semiconductor (O-DMS) for spintronics.

摘要

Single-phase (001) anatase thin films have been realized via epitaxial stabilization on (001) LaAlO3 substrates using reactive sputter deposition. Phase-pure anatase can be achieved using either water vapor or oxygen as the oxidizing species, although crystallinity is slightly degraded for films grown with water vapor. The use of hydrogen during growth to manipulate Ti valence appears possible, although controlling phase formation remains challenging.; The RF reactive sputtering method is used to prepare titanium dioxide thin films on Si(100) p-type at temperature ranging from 550 to 750°C. For the temperature range examined, only the rutile (200) phase was observed in the range of temperature between 600 and 650°C with Ar gas. The intensity of rutile (200) phase was much less with P(O2) than that with P(H 2O) at a total pressure of 15 mtorr with Ar gas. Hall coefficient and magnetoresistance results for the TiO2 on Si(100) with 10 -3 Torr of a water vapor at 300K shows typical n-type semiconductor behavior at 300K.; Epitaxial CoxTi1-xO2 anatase thin films were grown on (001)LaAlO3 by a reactive RF magnetron co-sputter deposition with water vapor serving as the oxidant. The use of water as the oxygen source proves useful in growing oxygen-deficient, semiconducting Co xTi1-xO2 by reactive sputter deposition, with undoped and Co-doped TiO2 thin films showing n-type semiconductor behavior, and carrier concentrations of 1017 to 1018 cm-3. Magnetization measurements of Cox Ti1-xO2 (x = 0.07) thin films reveal ferromagnetic behavior in the M-H loop at room temperature with a saturation magnetization on the order of 0.6 Bohr magnetons/Co. X-ray photoemission spectrometry indicates that the Co cations are in the Co2+ valence state. However, chemical analysis of surface structure indicates that the cobalt segregates into a Co-enriched particles on the surface of films.; From SADPs, we confirm that the nanoclusters observed on the surface of the Co0.07Ti0.93O2 are Co-enriched anatase.; From the resistivity measurement as a function of magnetic field, the ordinary Hall effect is dominant in the undoped and Co0.02Ti 0.98O2-delta thin films. For each film, the magnetoresistance was positive and increase monotonically with increasing magnetic field. The anomalous Hall effect contribution is observed for the Co0.10Ti 0.90O2-delta films grown under lower water vapor pressure due to more oxygen deficiency.