非磁性元素掺杂半导体铁磁性研究及其内禀属性鉴定方法

Spintronics devices are considered the best option for next generation microelectronic components since the spin related devices will have low power, high speed and flow a spin current without dissipation. Due to their freedom of both charge and spin, Diluted Magnetic Semiconductors (DMS) are believed to be primary materials for fabrication of spintronics devices. Currently, there are two big challenges for achieving a qualified DMS for spintronics devices. One is to avoid non-uniform magnetic field distribution caused by magnetic element clusters, other one is to prove intrinsic ferromagnetic property of DMS. This project is aim at development of non-magnetic element doped DMS by introducing a large quantity of carriers and defects, through the exchange interaction between carriers and localized moments (defects), to achieve room temperature carrier mediated ferromagnetism. In connection to identify intrinsic ferromagnetism, we will use low-energy muon spin rotation spectroscopy to determine the magnetic volume fraction of the sample in plane, polarized neutron reflectometry to provide the depth profiles of the magnetic moment distribution, X-ray Magnetic Circular Dichroism to probe the specific magnetic information of any selected element in the sample. Combined with first principles density functional theory (DFT) calculations, we can provide sufficient evidence of the existence of intrinsic ferromagnetism. Furthermore, it is of academic significance and technical importance to clarify the mechanism of ferromagnetism of non-magnetic element doped DMS. The influence of carriers and defect on magnetic and electric properties will be investigated to provide useful information for the design and fabrication of Spintronics devices.

由于自旋在操作中具有功率低、速度快和非易失性等优点，自旋电子器件被认为是下一代微电子元件的最佳选择，而稀磁半导体（DMS）因其兼具电荷态和自旋态两方面可调控自由度被认为是制造自旋电子器件的主要材料。目前，DMS的两大难题是如何防止磁性元素团簇所引起的非均匀磁场和如何证明铁磁性的内禀属性。本项目拟采用非磁性元素掺杂和缺陷工程，向氧化物半导体中引入大量载流子和晶格缺陷，通过载流子和具有磁矩的缺陷之间的交换作用，实现载流子介导的室温铁磁性。在鉴定内禀铁磁性方面，本项目拟采用μ介子自旋旋光谱来分析材料的磁化平面状态、极化中子反射来分析其磁化深度剖面，X射线磁性圆二色谱来探测其磁性来源，再结合第一原理计算，综合不同维度的磁性检测数据，从正面论证DMS铁磁性内禀属性的问题。研究磁电性能随载流子和缺陷变化的规律，揭示非磁性元素掺杂DMS铁磁性形成的机理，为今后自旋电子器件的设计与研发提供理论与试验参考。

自旋电子学在过去十年里一直处在一个非常活跃的领域。一个重要的原因是，兼具磁性和半导体属性的材料，为基于电子的自旋和电荷动力学的新型设备概念铺平道路。其中一个基本条件是在半导体中实现室温铁磁性。而氧化锌（ZnO）和二氧化钛（TiO2）是两种最有潜力实现载流子介导的室温铁磁性的DMS宿主材料。在本项目中，为了研究掺杂元素、晶格缺陷和载流子对DMS磁性的影响，我们采用PLD技术在不同基片上沉积了不同氧空穴浓度的非磁性元素掺杂ZnO薄膜，和磁控溅射技术制备多元素共掺杂的TiO2薄膜。并通过XRD检测样品的晶体结构和排除可能的第二相，用XPS揭示成分的化学状态，用SQUIDS检测薄膜的整体磁性，用PNR结合SMIS来研究样品中每个特定元素的分布和磁性分布的关系，用XMCD来寻找材料中磁性的源头，用μSR研究氧空穴对材料内部磁性分布的影响。结果表明：氧空穴能促使材料产生室温铁磁性；材料内部磁信号与载流子浓度有很高的关联度；材料内部磁体积分数随着沉积过程中的氧分压的增加而减少。