【作者】 姜鹏；

【导师】 蒋大鸣；

【作者基本信息】 哈尔滨工业大学 ， 材料科学与工程， 2013， 博士

【摘要】 集成电路是二十世纪最重要的科技成果之一，其推动了电子技术的高速发展。然而，由于工作时的电子迁移速率、功耗和散热等的制约，集成电路渐渐的不能满足人们对高速运算、低功耗以及大信息量传输的要求。和电子相比，光子不具有质量，且传输速率是电子的1500倍，因此光学器件的发展将对解决目前电子领域所面对的性能提升、功耗及散热等瓶颈具有革命性的影响。集成光学器件相对于分立元件构成的系统具有更高的效率，运算速度和经济性。因此伴随着光通信产业的快速发展，将所有的光学元件（如：激光发生器，调制器，波导和探测器等）集成到Si或者是III-V半导体平台上的光电集成技术引起了持续的关注。然而，非可逆光学器件，尤其是集成光隔离器，由于缺乏一种可以与半导体基体匹配良好的高品质因子的磁光材料，成为集成光学器件中唯一缺失的器件。本文采用激光脉冲沉积技术，在（LaAlO₃）_0.3（Sr₂AlTaO₆）_0.7--LSAT基体上制备了Fe掺杂SrTiO₃钙钛矿磁光薄膜，研究了不同Fe掺杂含量、激光能量密度和沉积厚度对薄膜的晶体结构、磁性、光学性能和磁光性能的影响。Fe掺杂SrTiO₃薄膜中Fe原子取代了B位的Ti原子，薄膜的晶格结构为钙钛矿外延结构，无第二相及杂质相的存在。随着Fe掺杂含量的升高，晶格常数c而变大，c/a同时变大，薄膜整体受压应力；同时Sr(Ti_1-xFe_x)O₃薄膜的饱和磁化强度（Ms）随之升高，当Fe掺杂含量达到40%达到最大值。薄膜的矫顽力和各向异性场随着Fe含量的升高而变大。铁磁性产生的机理主要是由于Fe-O-Fe离子对之间存在的超交换（super-exchange）及双交换（double-exchange）效应。饱和法拉第旋光随着Fe含量的增加而增强，变化规律与磁化曲线一致。随着Fe含量的增加，Sr(Ti_1-xFe_x)O₃薄膜在可见光和红外部分的光透过率随之增加，同时薄膜的能带间隙随着Fe含量的增加而变。Fe在B位掺杂含量达到40%的Sr(Ti_0.6Fe_0.4)O₃--STF40薄膜具有较高的品质因子，约为1.1-1.3deg/dB。随着激光能量密度的升高，Sr(Ti_0.6Fe_0.4)O₃薄膜的晶格常数c及异方度（c/a）随之降低；同时，薄膜的饱和磁化强度、矫顽力、薄膜的各向异性场以及饱和法拉第旋光也随之降低。随激光能量密度的升高，薄膜在可见光及红外部分的光学透过率随之提高。当薄膜厚度较小时，薄膜为单峰结构；当薄膜厚度超过临界值时，由于应力松弛，出现了双峰结构。钙钛矿薄膜可以通过缓冲层CeO2/YSZ在Si基片上延生长，其生长在CeO2上不是“cubic-on-cubic”的生长方式，而是旋转45°后STF40的晶格的对角线与CeO2晶格的邻边上的原子相互匹配。薄膜与基体均为外延生长的钙钛矿结构，薄膜无第二相和杂质相的存在。在CeO₂/YSZ/Si生长的薄膜的磁性能与LSAT基片上生长的薄膜具有相似的磁性能。在Sr(Ti_0.6Fe_0.4)O₃薄膜的基础上，通过阳离子掺杂方法在A位掺杂La、Ce原子及在B位掺杂Zr、Ga原子，研究其对薄膜的晶格结构、物理性能以及品质因子的影响。结果发现，A位掺杂Ce、La原子，薄膜为钙钛矿外延结构，晶格常数c随着Ce、La掺杂含量的升高而变大，c/a同时变大。薄膜中无第二相及团簇存在；元素分布均匀，界面处无元素扩散。XPS结果发现，A位掺杂La、Ce元素取代了钙钛矿晶格结构中的A位的Sr2+，并作为施主为薄膜提供了自由电子。薄膜的导电性随着La、Ce掺杂含量的增多而升高；同时，薄膜的光学能隙变大，费米能级向高能级移动；Fe与Ti的价态向低价态转变。薄膜的磁性能及磁光性能随着Ce、La掺杂含量的升高而变大；而光学透光率随着Ce、La掺杂含量的升高而变小。薄膜的低温磁性能表明，薄膜具有自旋玻璃态（spin-glass）行为。薄膜的零场冷却曲线的峰值温度随着磁场强度的升高而降低，且与薄膜所受的应力状态有关。A位施主掺杂由于光学透过率的下降，并未提高薄膜的品质因子。B位Ga原子掺杂Sr(Ti_0.6Fe_0.4)O₃薄膜为受主掺杂，其晶格常数c、饱和磁化强度、矫顽力、各向异性场以及饱和磁光性能随着Ga掺杂含量的升高而降低。由于随着Ga含量的升高，Fe及Ti的价态向高价态变化，薄膜的光学透过率随之升高。B位Zr原子掺杂Sr(Ti_0.6Fe_0.4)O₃薄膜，由于Zr离子的平均价态高于Ti离子，表现为施主掺杂。薄膜为钙钛矿外延薄膜，且薄膜的晶格常数c随着Zr含量的升高而变大，c/a同时变大。薄膜随着Zr含量的增多，薄膜中Fe和Ti的价态随之降低。薄膜的饱和磁化强度及法拉第旋光性能先升高后降低，在Zr含量为20at.%时候达到最高值。薄膜的光学性能随着Zr原子的掺杂而降低。研究表明，Fe:SrTiO₃薄膜的品质因子受到Fe及Ti元素的价态影响显著。施主掺杂由于降低了薄膜中Fe及Ti离子的价态，从而严重影响了光学透过率，降低了薄膜的品质因子。受主掺杂可以提高薄膜的光学透过率，从而提高了薄膜的品质因子。Sr(Ti_0.2Ga_0.4Fe_0.4)O₃薄膜具有较高的品质因子，约为4⁶.7deg/dB，可以成为集成光隔离器的重要候选材料。更多还原

【Abstract】 The integrated circuit, which is one of the most important scientific andtechnological achievements of the20thcentury, promoted the rapid development ofelectronic technology. However, due to the constraints of the electron mobility in thework rate, power consumption and heat dissipation, etc., integrated circuitsgradually can not meet the requirements for high-speed operation, low powerconsumption, as well as a large amount of information transmission.Compared withelectrons, photons have no mass and the transmission rate is1500times than theelectron, so the development of optical devices will have the revolutionary influenceto solve the present power consumption, heat dissipation and bottleneck ofperformance improvement. Integrated optical device have higher efficiency,operation speed and economy advantage compare with system composed by discretecomponents. Therefore, to integrate the optical device elements such as lasergenerator, modulator, optical waveguide and detector on Si or III-V semiconductorsubstrates has attracted wide attention. However, Nonreciprocal photonic devicesincluding optical isolators and optical circulators are the only absent integratedoptical device due to absence of magneto-optical materials which both have thegood figure of merit and matching ability with semiconductor substrates such as Si.In the present work, the crystal structure, magnetic, optical and magntoopticalproperties of Fe:SrTiO₃perovskite films grown on （LaAlO₃）_0.3（Sr₂AlTaO₆）_0.7--LSATsubstrate with different Fe contents, laser energy density and depositional thicknesswere investigated. The Fe doped SrTiO₃films which B sites substituted by differentFe contents, were perovskite-structureepitaxial films and no second phase orimpurity phase. With increasing Fe concentration, lattice parameters c and c/a ratiowere increased. The films showed in-plane compressive stress. The saturationmagnetization （Ms）, increased with increasing Fe concentration and reachedmaximum when Fe concentration was40%. The coercivity fields and anisortropyincreased with Fe content. The mechanism for room temperature ferromagnetismwas mainly Super-exchange and Double-exchange effects between Fe-O-Fe ionpairs. The saturation Faraday rotation increased with increasing Fe content whichconsistent with magnetization curve. The optical transmittance at both visible andinfrared wavelength increased with increasing Fe content, meanwhile, the band gapincreased. The Sr(Ti_0.6Fe_0.4)O₃--STF40film which40at.%Fe doped into B siteshave good figure of merit,¹.1-1.3deg/dB.With the increasing laser energy density, the lattice parameters c and c/a ratioof STF40film decreased, meanwhile, the saturation magnetization, coercivity fields,anisortropy and saturation Faraday rotation were also decreased. The optical transmittance at both visible and infrared wavelength increased with increasing laserenergy density. The XRD of film was single peak when the depositional thicknesswas thin. When the film thickness exceeded a critical value, the strain was partiallyrelaxed and became double peaks in XRD.The STF40perovskite film grown on Si substrate by CeO2/YSZ buffer layerwhich lattice diagonal atoms of films after rotate45°matched with lattice adjacentedges instead of cubic on cubic method. Both the film and substrate wereperovskite-structure epitaxial films without second phase or impurity phase. Thefilms grown on CeO2/YSZ/Si had similar magnetic properties with that on LSAT.The effect of A site La,Ce and B site Zr, Ga doped Sr(Ti_0.6Fe_0.4)O₃by cationdoping method on crystal structure, physical properties and figure of merit wereinvestigated. The results showed that the A site La, Ce doped Sr(Ti_0.6Fe_0.4)O₃filmswere perovskite epitaxial films. The lattice parameters c and c/a ratio of the filmsincreased with increasing La,Ce concentration.There were no second phase andcluster in the films, the elements distribution of films were homogeneous withoutelements diffusionat the interface of films and substrates. The XPS results show thatCe ions showed a dominant3+valence state, and acted as donors on the Sr2+site （Asite） in the perovskite lattice.Ce Theoptical band gap widened and the Fermi levelmoved toward the vacuum level with increased or La content;meanwhile the Ti andparticularly the Fe ions were driven to a lower valence state. The saturation Faradayrotation increased with increasing La, Ce concentration which consistent withmagnetization curve. The optical transmittance at both visible and infraredwavelength decreased with increasing La, Ce content. The low temperaturemagnetic properties of the films showed spin-glass behavior. The peak position ofzero-field-cooling curves of films shifted with strain state. The figure of merit of Asite La, Ce doped Sr(Ti_0.6Fe_0.4)O₃were not improved due to rapid decreasing ofoptical transmittance.The lattice parameters c, the saturation magnetization,coercivity fields,anisortropy and saturation Faraday rotationof Ga Substituted Sr(Ti_0.6Fe_0.4)O₃in Bsite which acted as acceptors decreased with increasing Ga concentration. The Tiand the Fe ions were driven to a higher valence state, and the optical transmittanceincreased with increasing Ga contents. The Zr Substituted Sr(Ti_0.6Fe_0.4)O₃in Bsiteacted as donors due to the average valence state of Zr was higher than that of Ti.The films were perovskite films, and the lattice parameters c and c/a ratioincreased with increasing Zr contents. The Ti and the Fe ions were driven to a highervalence state. The saturation magnetization increased at first and then decreasedwhich reach the maximum at20at.%Zr content. The optical transmittance decreased with increasing Zr contents.In conclusion, the Fe and Ti valence state played a important role in figure ofmerit of the Fe doped SrTiO₃perovskite films. The figure of merit and opticaltransmittance of donor doped Fe:SrTiO₃decreased due to the Ti andFe ions weredriven to a lower valence state. The figure of merit a of acceptor doped Fe:SrTiO₃increased due to the improvement of optical transmittance. The figure of merit ofSr(Ti_0.2Ga_0.4Fe_0.4)O₃could reach4⁶.7deg/dB which could be important candidatefor integrated optical isolators.更多还原