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Local Structure and Magnetic,Transport Properties of In2O3-based and SiC-based Dilute Magnetic Semiconductor Films

Author: DuanLingShen
Tutor: AnYuKai
School: Tianjin University of Technology
Course: Materials Physics and Chemistry
Keywords: In2O3 SiC DMS Local structure Magnetic properties Transport properties
CLC: O484.1
Type: Master's thesis
Year: 2012
Downloads: 57
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Abstract


Diluted magnetic semiconductors （DMSs） have been attracted a great deal of attentiondue to the possibility of intengrating charge and spin degree of freedom and therefore havecharacteristic of both magnetism and semiconductor. At the same time, as candidates for usein spintronics applications, DMSs have been intensive studied. At present, DMS is still in thestage of study, and problems mainly focus on two aspects, the origin of magnetism andmagnetic adjustment mechanism. If we can solve these problems, the technology of electronicinformation maybe will have great progress.In this paper, by RF magnetron sputtering techniques, we deposited the Mn and Co dopedIn2O3-base DMS films as well as Cr-doped or Cr, Mn-codoped SiC-base DMS films. Localstructure, magnetic and transport properties were investigated by XRD, SEM, XPS, XANES,EXAFS, PPMS, HALL, R-T, PL and U-V et al.. The main results are:1. Local structure, magnetic and transport properties of Mn doped In2O3film are investigated.The results showed that the Mn-doped In2O3films have a Cubic Bixbyite Structure, and Mn2+ions are incorporated into the In sites of lattice. There do not exist Mn cluster, second phaseoxide and interstitial Mn atoms in the films. In5at%,8.5at%and13.7at%Mn-doped In2O3films, the strength of p-d hybridization of Mn3d and O2p orbits is weakened in turn. Thecarriers concentrations of Mn-doped In2O3films with different Mn-doped concentration areabout1*1018cm-34*1018cm-3. The conductive mechanism can be fitted by the model ofMott’s VHR. With the increase of Mn doping concentration, the resistivity increases firstlyand then decreases, and forbidden band width decreases. The Mn-doped In2O3films withdifferent doped concentrations all have obviously room-temperature ferromagnetism. Andwith increasing Mn doped concentrations, the saturation magnetization firstly increases, thendecreases when the Mn-doped concentrations are beyond of8.5at%. According to thefollowing results, we suggest a possible room-temperature magnetism mechanism, namelythere exists a strong p-d hybridization coupling between Mn3d electron and O2p electron,which resulting in the polarized of O2p electron. The polarized O2p electron can transitionto other Mn p-d hybridization orbits, and exchange the spin with other Mn3d electron, andobtain the long-range magnetic order in the end.2. Local structure, magnetic and transport properties of Co doping In2O3film samples areexplored. The results show that all Co-doped In2O3films formed Cubic Bixbyite Structure,most of Co atoms are incorporated into the In sites of the In2O3lattice in the form of Co2+ions,and a small amount of Co atoms form the Co cluster. There are no second phase oxide andinterstitial Co atoms in the films. The carriers concentrations of all Co-doped In2O3films isabout3*1018cm-31.7*1019cm-3. The conductive mechanism can be fitted by the model ofMott’s VHR. With the increase of Co doping concentration, the resistivity decreases. Differentconcentration Co-doped In2O3films reveal the room ferromagnetism. And with the increase of Co doping concentration, saturation magnetization intensity increases first and thendecreases. According to the test results, Co cluster contribute to magnetism, but is not theonly source. And direct exchange, RKKY indirect exchange and BMP model can not explainthe magnetism change rule. Therefore, room temperature magnetism associated with Cocluster and VRH conductive mechanism.3. Local structure, magnetic and transport properties of the Cr-doped and Cr, Mn co-dopedSiC are investigated. For the Cr-doped SiC films, some Cr atoms form Cr cluster, and othersome Cr atoms substitute Si or C atoms. Carrier concentrations of the as-deposited Cr-dopedSiC films with different doped concentrations are about2*1020cm-31.4*1021cm-3. Withincreasing Cr-doped concentrations, the resistivity of films decreases. The conductivemechanism of5at%Cr-doped SiC films can be fitted by the model of Efros’s VHR. For Cr,Mn co-doped SiC films annealed at different temperatures, it can be found that parts of Cr andMn atoms substituted for C or Si sites of lattice, and other some formed Cr or Mn cluster. TheXRD results show that the （111） interplanar distance of SiC films increased with increasingMn doped concentrations, but the Cr and C cluster can decrease. When Mn dopedconcentrations reached to6%, the （111） interplanar distance decrease and the CrMn secondphase appeared. It is also found that with the increase of Mn doping concentration, carrierconcentrations of Cr, Mn co-doped SiC films increase and resistivity decrease, respectively.At the same time, the saturation magnetization increases firstly and then decreases, but theMn doping can obviously enhance the saturation magnetism of the films. According to theinvestigation of local structure, magnetic and transport properties of Cr, Mn co-doped SiCfilms, it can be considered that the magnetism of the as-deposited and1200℃annealed Cr,Mn co-doped SiC films has strong correlation with the Cr and Mn atoms substituted at Si sitesas well as BMP mechanism.

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CLC: > Mathematical sciences and chemical > Physics > Solid State Physics > Thin Film Physics > Film growth,structure and epitaxy
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