Synthesis, Structure and Properties of III-V Ferromagnetic Semiconductor Thin Films

技术：铁磁性III-V族半导体的发展为一类具有磁性、磁光和半导体特性的多功能材料提供了潜力。这些材料提供了操纵自旋和电荷的潜力。然而，由于它们的低转变（居里）温度，它们的利用受到阻碍。最近有报道称，铁磁半导体的居里温度超过300 K。越来越多的证据表明，在某些铁磁性半导体中，无序对稳定铁磁性起着至关重要的作用。关于稳定高温铁磁相的详细机制和磁性物质的性质的问题出现了。本项目将开发窄带隙铟基III-V型铁磁半导体薄膜，包括InMnAs和InMnSb及其固溶体。特别令人感兴趣的是过渡金属原子团簇在稳定这些半导体的高温铁磁性中所起的作用以及短程有序的性质。进一步研究了自由载流子浓度对铁磁相稳定性的影响。本项目将采用金属有机气相外延（MOVPE）技术合成外延合金薄膜。制备不同锰浓度的半导体合金，以确定无序在稳定铁磁性中的作用。最新的基于独立分解形成铁磁团簇的模型将被测试。要使用的实验表征技术包括温度和场相关的磁化测量，霍尔效应和磁阻。磁光克尔效应（MOKE）及其在中红外到可见光区域的光谱依赖性将用于确定合金中交换相互作用的性质和大小。先进光子源的x射线吸收光谱和x射线磁圆二色性（XMCD）将用于确定组成合金的元素的磁性能。扩展x射线精细结构分析（EXAFS）、分析电子显微镜和具有原子尺度分辨率的电极原子探针将用于确定簇的大小和分布。将比较由结构和磁测量确定的簇大小。非技术：该项目涉及材料科学领域的基础研究问题，具有很高的技术相关性，并有望为铁磁半导体材料提供科学的理解，并有望应用于自旋器件，如自旋阀、磁性随机存取存储器和量子计算。该项目为研究生和本科生提供跨学科主题的培训，包括半导体物理和磁学。该项目还包括向当地学校开展教育外展活动，并与国家实验室合作，为学生提供更多的学习机会。

Technical: The development of ferromagnetic, group III-V semiconductors has provided the potential for a class of multifunctional materials that exhibit magnetic, magneto-optical, and semiconducting properties. These materials offer the potential for manipulating both spin and charge. Their utilization, however, has been impeded due to their low transition (Curie) temperatures. Recently there have been reports of ferromagnetic semiconductors with Curie temperatures in excess of 300 K. There is growing evidence that disorder plays an essential role in stabilizing ferromagnetism in certain ferromagnetic semiconductors. The question arises as to the detailed mechanism for stabilizing the high temperature ferromagnetic phase and the nature of the magnetic species. In this project, narrow bandgap indium based III-V ferromagnetic semiconductor thin films will be developed, including InMnAs and InMnSb and their solid solutions. Of specific interest is what role transition metal atomic clusters play in stabilizing high temperature ferromagnetism in these semiconductors and the nature of the short range order. Furthermore the role of free carrier concentration on the ferromagnetic phase stability will be examined. During the project, epitaxial thin alloy films will be synthesized by metalorganic vapor phase epitaxy (MOVPE). Semiconductor alloys with different manganese concentrations will be prepared to determine the role disorder plays in stabilizing ferromagnetism. Recent models based on spinodal decomposition forming ferromagnetic clusters will be tested. Experimental characterization techniques to be used include temperature and field dependent magnetization measurements, Hall effect, and magnetoresistance. The magneto-optical Kerr effect (MOKE) and its spectral dependence over the mid infrared to visible region will be used to determine the nature and magnitude of the exchange interaction in the alloys. X-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) at the Advanced Photon Source will be used to determine the magnetic properties of the elements comprising the alloys. Extended x-ray fine structure analysis (EXAFS), analytical electron microscopy, and an electrode atom probe with atomic scale resolution will be used to determine cluster size and distribution. Comparisons will be made between cluster sizes determined by structural and magnetic measurements.Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance, and is expected to provide scientific understanding of ferromagnetic semiconductor materials with potential applications for spin based devices such as spin valves, magnetic random access memories, and quantum computation. The project provides training of graduate and undergraduate students in an interdisciplinary topic, consisting of semiconductor physics and magnetism. The project also includes educational outreach activities to local schools and collaboration with national laboratories, which provide enhanced learning opportunities to students.