The Preparation, Structure And Properties Of Co And Mg Co-doped In₂O₃ Diluted Magnetic Semiconductor Films

In this paper,the Co/Mg co-doped In₂O₃ diluted magnetic semiconductors?DMSs?films were deposited on SiO₂/Si?100?and super white glass substrates by RF-magnetron sputtering.The local structure,spin-dependent magnetic and transport properties of In₂O₃ based DMS films were investigated systemically by X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Transmission electron microscopy?TEM?,X-ray absorption fine structure?XAFS?,Hall effects,resistivity-temperature curves?R-T?and magnetic measurements?SQUID?,the main results are following:1.We have deposited a series of(In_0.97-xCo_xMg_0.03)₂O₃ films.The detailed structural analyses suggest that all the films have a cubic bixbyite structure,no traces of Co metal cluster and related oxide secondary phases were observed.The XPS and HRTEM images showed that both Co and Mg elements present valence state of +2 and the films are highly oriented and exhibited a clear fringe spacing.Besides,the doped Co ions mainly exist in the substitutional form and a part of element Co form the metal clusters from the results.The full multiple-scattering ab initio calculations indicate that all the doped Co ions substitute for In3+sites of In₂O₃ lattice and the nearest-neighbor coordination shell existed oxygen vacancies when x=0.02.What's more,the relative concentrations of Co at substitutional sites increase then decrease with further increasing Co concentration.The Hall measurements indicated that all films possess n-type conductivity and the carrier concentration nc decreases then increases with Co doping concentration.The transport properties measurements show that all the films show semiconducting behavior.The electronic conducting mechanism is dominated by Mott variable range hopping?VRH?behavior at low temperature and Hard bandgap hopping behavior at high temperature.The magnetoresistance?MR?measurements indicate that the film with Co concentration x=0.02,0.04 only show a negative MR component at different temperatures.With further increasing Co concentration up to x=0.085,the resistivity of films increase then decrease,whereas the MR always keep positive.The UV transmission spectra measurements show the transmittance intensity of films decreases with the increases of Co concentration.Magnetic characterizations show that all the films show intrinsic room-temperature?RT?ferromagnetism and Ms increases then decreases with Co doping.However,The carrier concentration shows different changing tendency compared with resistivity and the room temperature ferromagnetism induced by the mediated carriers is ruled out.The room temperature ferromagnetism can be ascribed to oxygen-induced bound magnetic polarizations.For films with high Co doping concentration,the relative percentage of Co at substitutional sites decrease,which leads to the decreasing of the bound magnetic polarons induced dy the Vo,then the Ms weakened.2.We have deposited a series of (In_0.98-yCo_0.02Mg_y)₂O₃ films.The detailed structureshows that the co-doped In₂O₃ films have a cubic bixbyite structure,no traces of Co or Mg metal clusters and related oxide secondary phases were observed.When the doped concentration y=0.03,a part of element Co form the metal clusters for the film,while the metal clusters vanished with the increasing of Mg concentration.The Hall measurements indicated that all films possess n-type conductivity and the carrier concentration nc decreases and the resistivity increases gradually as a function of Mg concentration.All the films show semiconducting behavior and the electronic conducting mechanism is dominated by Mott variable range hopping?VRH?behavior at low temperature and Hard bandgap hopping behavior at high temperature.The transmittance intensity of films and the band gap increases with the increases of Mg concentration,resulting in an obvious blue shift in the absorption edge position.The magnetoresistance?MR?changes form negative MR into a positive MR.When the concentration increased up to y=0.06,the film shows the positive MR component at 10 K and the MR transforms into negative MR behavior again for the higher temperature,which indicates there is a relationship between the temperature and the sign of MR.Magnetic characterizations show that all the films are intrinsic RT ferromagnetism and the Ms increases then decreases with Mg doping.The interaction between the doped Co ion has a strong connection with oxygen vacancies,which induces the formation of bound magnetic polarons.All the results indicate that the room-temperature intrinsic ferromagnetism is ascribed to the bound magnetic polarons model.