【作者】 段岭申；

【导师】 安玉凯；

【作者基本信息】 天津理工大学 ， 材料物理与化学， 2012， 硕士

【摘要】 稀磁半导体（DMS）因兼具半导体和磁性的特点，即在同一种材料中同时应用电子自旋和电子电荷两种自由度，而受到广泛关注。同时，其作为自旋电子学器件的后备材料，迅速成为研究的热点。目前，DMS尚处于研究阶段，存在的问题主要集中在磁性来源和磁性调节机制两个方面。如果能解决这些问题，必将给未来电子信息技术的发展带来巨大影响。本论文采用射频磁控溅射法分别制备了不同浓度Mn、Co掺杂In₂O₃基稀磁半导体薄膜，以及不同浓度Cr掺杂或Cr、Mn共掺杂SiC基稀磁半导体薄膜。并利用XRD、SEM、XPS、XANES、EXAFS、PPMS、HALL、R-T、PL以及U-V等手段对薄膜进行一系列的结构表征及自旋相关磁、输运特性的研究。获得的主要成果如下：1、研究了不同Mn浓度掺杂In₂O₃薄膜样品的局域结构及磁、输运性能。结果发现：不同Mn掺杂浓度In₂O₃薄膜全部形成了方铁锰矿结构，Mn元素以Mn2+离子替位In3+的形式进入In₂O₃晶格，薄膜中不存在Mn团簇，Mn的第二相氧化物及间隙Mn原子等。对于不同Mn掺杂浓度In₂O₃薄膜，Mn3d与O2p杂化耦合程度为5at%最高，8.5at%次之，13.7at%最低，其载流子浓度约1×10¹8cm^-34×10¹8cm^-3，导电机制符合Mott的变程跃迁模型。电阻率随Mn掺杂浓度的增加先增加后减小，禁带宽度随Mn掺杂浓度增加而减小。不同Mn掺杂浓度In₂O₃薄膜均具有室温铁磁性，饱和磁化强度随Mn掺杂浓度的增加先增加后减小。根据这些表征和测试结果，我们提出了一种可能的铁磁性产生机理，即Mn3d电子通过与O2p电子的耦合杂化，使2p电子极化，且2p电子被极化的概率与杂化程度有关，然后2p电子通过变程跳跃模式，在一定范围内跃迁到能级相近的Mn原子杂化轨道上，进行自旋交换，从而实现长程磁有序。2、研究了不同Co掺杂浓度In₂O₃薄膜样品的局域结构及磁、输运性能。不同Co掺杂浓度In₂O₃薄膜全部形成了方铁锰矿结构，Co元素主要以Co2⁺离子替位In3+的形式进入In₂O₃晶格，薄膜中不存在Co金属氧化物第二相和间隙Co原子，但是形成了少量Co团簇。对于不同浓度Co掺杂In₂O₃薄膜，其电阻率随Co掺杂浓度的增加而减小，载流子浓度约3×10¹8cm^-31.7×10¹9cm^-3，导电机制符合Mott的变程跃迁模型。不同Co掺杂浓度In₂O₃薄膜均具有室温铁磁性，饱和磁化强度随Co掺杂浓度的增加先增加后减小。根据测试结果，Co团簇对Co掺杂In₂O₃的磁性有一定贡献，但并不是唯一来源，而且直接交换、载流子为媒介的RKKY理论和束缚磁极子（BMP）模型均不能解释其磁性变化规律。因此，我们仍然支持变程跃迁调节长程磁有序的观点。3、研究了制备态、800℃退火和1200℃退火的Cr掺杂以及Cr、Mn共掺杂SiC稀磁半导体薄膜的局域结构和磁、输运性能。对于不同浓度Cr掺杂SiC薄膜，一部分Cr元素形成Cr团簇，另一部分则替位了SiC晶格中的C原子和Si原子，且以替位Si为主。制备态的不同Cr掺杂浓度SiC薄膜的载流子浓度约2×10²0cm^-31.4×10²1cm^-3，5at%Cr掺杂SiC薄膜的导电机制符合Efros的变程跃迁模型，且电阻率随Cr掺杂浓度的增加而减小。对于Cr、Mn共掺杂SiC薄膜，不同退火温度下，Cr、Mn元素均以单质态和C替位或Si替位态存在。XRD研究发现，随着Mn掺杂浓度的增加，Cr、Mn共掺杂SiC薄膜（111）面间距增大，同时Cr团簇和C团簇减少。当Mn掺杂浓度达到6%，超出Cr、Mn在SiC中的溶解度时，析出CrMn第二相，同时（111）面间距减小。Cr、Mn共掺杂SiC薄膜随Mn掺杂浓度的增加载流子浓度增大，电阻率减小，饱和磁化强度则先增大后减小，且Mn的掺入使铁磁性明显增强。结合局域结构及磁、输运性能测试结果可以认为：Cr、Mn共掺杂SiC薄膜制备态和1200℃退火态样品磁性均来Cr、Mn替位Si原子，磁性大小受束缚磁极子调节。更多还原

【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.更多还原