Local Structure And Magnetic, Transport Properties Of In₂O₃Diluted Magnetic Oxide-semiconductors

Because the Inium oxide (In2O3) diluted magnetic oxide semiconductors combines thecentralized of optical properties, electrical properties, magnetic properties in one, it has a verybroad application prospects. In recent years, how to control the various properties of In2O3made people do a lot of researches. However, there are many problems to be solved in furtherstudies such as the local structure, spin-dependent magnetic and transport properties of thedoped magnetic ions.In this paper, the Cr-doped In2O3, Fe/Cu co-doped In2O3and Co/Cu co-doped In2O3diluted magnetic semiconductors (DMS) films were deposited on SiO2/Si (100) substrates byRF-magnetron sputtering technique. The structure and physical properties of these films havebeen investigated systemically by X-ray diffraction(XRD), X-ray photoelectronspectroscopy(XPS), X-ray absorption fine structure(XAFS), Hall effects, resitivity-temperature curves(R-T), and magnetic measurements(SQUID). Here are the results:1. The structural analysis of Cr-doped In2O3films clearly indicates that Cr ions substitutefor In3+sites of the In2O3lattice in the valence of+2states, and the exist of Cr-related clustersor oxides secondary phases is safely ruled out. Accordding to the multiple-scatteringcalculations results of Cr K-edge, the nearest coordination shell of Cr ions is complexed withoxygen vacancies. The films with low Cr concentration show a crossover fromsemiconducting to metallic transport behavior, whereas only semiconducting behavior isobserved in high Cr concentration films. The transport property of all films is governed byMott variable range hopping behavior, suggesting that the carriers are strongly localized.Magnetic characterizations show that the saturated magnetization of films increases first, andthen decreases with Cr doping, while carrier concentration decreases monotonically, implyingthat the ferromagnetism is not directly induced by the mediated carriers. It can be concludedthe ferromagnetism of films is intrinsic and originates from bound magnetic polarons modelassociate with oxygen vacancies.2. The structural and magnetic-transport properties of the Fe/Cu co-doping In2O3filmshave been investigated systematically. The detailed structure analysis suggest that Fe ionssubstitute for In3+sites of the In2O3lattice in the mixed valence state of+2and+3, and thenearest coordination shell existed oxygen vacancies, we can safely ruled out the existence ofFe-related clusters or oxides secondary phases. Cu presence of Cu elemental or Cu relatedoxides, and did not enter the In2O3lattice. The films with low Fe concentration show acrossover from semiconducting to metallic transport behavior, whereas only semiconductingbehavior is observed in high Fe concentration films. The conductive mechanism meets theMott variable range hopping model within low temperature range，and dominated with thehard-band transition mechanism in high temperature range. These films show typical room temperature ferromagnetism, the saturation magnetization increases, while carrierconcentration decreases monotonically with Fe doping, implying that the ferromagnetism isnot induced by the carriers-mediated RKKY mechannism. The UV transmition spectrasuggested that the optical bandgap of these films decreases monotonically with the increase ofFe concentration. It can be concluded that the ferromagnetic order in Fe/Cu co-doped In2O3films is intrinsic, arising from Fe atoms substitution for the In sites of In2O3lattice. Theoxygen vacancies play a mediation role on the ferromagnetic couplings between the Fe ions,it suggested that the ferromagnetism is originated from bound magnetic polarizations.Elemental Cu or Cu oxides may inhibit the generation of ferromagnetic interaction throughshrink the range of the bound magnetic polarons, and the reducing of the oxygen vacanciesmay lower the number of bound magnetic polarons.3. The structural and magnetic-transport properties of the Co/Cu co-doping In2O3filmshave been investigated systematically. The structure analysis suggest that most of the dopedCo ions substitute for In3+sites of the In2O3lattice in the valence state of+2, and the nearestcoordination shell existed oxygen vacancies, but there presence small amount of them formedelemental Co, and Co-related oxide secondary phases in these films is safely ruled out. It alsosuggested that all the doped Co atoms substitute for In3+sites of the In2O3lattice with theincreasing of oxygen partial pressure. Cu presence of Cu elemental or Cu related oxides, anddid not enter the In2O3lattice. All these films showed the semiconducting behavior, and theconductive mechanism meets the Mott variable range hopping model within low temperaturerange，and dominated with the hard-band transition mechanism in high temperature range. Allof them show typical room temperature ferromagnetism. The saturation magnetization Msdecreases, while carrier concentration decreases monotonically with Co doping, implying thatthe ferromagnetism is not directly induced by the mediated carriers. The optical bandgap offilms decreases monotonically with the increase of Co concentration. It can be concluded thatthe ferromagnetic order in Co/Cu co-doped In2O3films is intrinsic, arising from Co atomssubstitution for the In sites of In2O3lattice. It suggested that the oxygen vacancies play animportant role on the ferromagnetic couplings between the Co ions, and the bound magneticpolarons model is still applicated. Elemental Co, elemental Cu or Cu oxides and the reducingof oxygen vacancies could inhibit the generation of ferromagnetic.