Spin Electronics: High Temperature Ferromagnetic Semiconductor Materials and Devices

这项拨款是由工程局的电气和通信系统司以及化学和运输系统司共同资助的。该提案是根据21世纪自旋电子学倡议（项目征求NSF 02-036）收到的。该提案的重点是稀释磁性半导体（DMS），这是未来利用电荷和电子自旋的电子和光电设备的有前途的材料。这些材料在自旋阀、非易失性磁随机存取存储器、量子计算和其他自旋极化输运和光器件中具有潜在的用途。最近的工作主要集中在III-V型DMS上，它们表现出优异的低温铁磁性能。目前已经实现了居里温度为105k的DMS取代III-V合金，但由于难以制备高居里温度和高磁化强度的材料，限制了其在薄膜异质结构中的应用。然而，铁磁半导体外延的最新进展表明，具有高居里温度的III-V材料应该是可以实现的。此外，包括伪III-V化合物II-IV-V2黄铜矿在内的其他半导体体系最近也被证明具有较高的居里温度。我们提出的工作建立在我们最近通过金属有机气相外延（MOVPE）制备的转变温度超过300 K的InMnAs合金以及我们发现的高Tc II-IV-V2化合物的基础上。MOVPE可以制备具有高磁化强度的III-V DMS，这是块体技术无法实现的。要研究的具体体系包括：InMnAs和II-IV-V2化合物ZnMnP2和MnGeP2。虽然这些半导体已经显示出相当大的前景，但磁性物质的性质还没有得到很好的理解。在该计划中，DMS晶体、薄膜和量子结构将在一定范围的磁性离子浓度下沉积，以优化居里温度和磁化强度。原子结构和磁性之间的关系将被确定，并与理论进行比较。这些计算将使用高精度的完全线性化增广平面波（FLAPW）方法。特别感兴趣的是磁性离子聚集发生的程度及其在高居里温度合金形成中的作用。实验技术包括高分辨率透射电子显微镜、扩展x射线精细结构分析（EXAFS）、温度和场相关磁化测量、霍尔效应和磁光测量。将制备几种薄膜自旋电子和光电异质结构，并测量其自旋相关性质。该计划将包括对磁性半导体材料和器件研究的博士研究生和本科生的培训。桑迪亚国家实验室和西北大学的合作。大学将进一步发展。将与韩国蔚山大学进行国际合作。

This grant has been co-funded by the Division of Electrical and Communications Systems, and the Division of Chemical and Transport Systems in the Engineering Directorate. This proposal was received in response to the Spin Electronics for the 21st century initiative, Program Solicitation NSF 02-036. The proposal focuses on diluted magnetic semiconductors (DMS), which are promising materials for future electronic and opto-electronic devices that utilize both the charge and the spin of electrons. These materials have potential uses in spin valves, non-volatile magnetic random access memories, quantum computation and other spin polarized transport and optical devices. Much of the recent work has focused on the III-V DMS which have shown excellent low temperature ferromagnetic properties. DMS substitutional III-V alloys with Curie temperatures of 105 K have been realized Their utilization in thin film heterostuctures, however, has been limited because of difficulties in preparing materials with both a high Curie temperature and magnetization. Nevertheless, recent advances in the epitaxy of ferromagnetic semiconductors indicate that III-V materials with high Curie temperatures should be realizable. Furthermore other semiconductor systems including the pseudo III-V compounds II-IV-V2 chalcopyrites have been recently shown to have high Curie temperatures. The proposed work builds upon our recent demonstration of InMnAs alloys with transition temperatures in excess of 300 K prepared by metal-organic vapor phase epitaxy (MOVPE) as well as our discovery of high Tc II-IV-V2 compounds. MOVPE enables the preparation of III-V DMS with high magnetization not possible by bulk techniques. Specific systems to be investigated include: InMnAs, and II-IV-V2 compounds ZnMnP2 and MnGeP2. While these semiconductors already show considerable promise, the nature of the magnetic species is not well understood. In the proposed program DMS crystals, thin films and quantum structures will be deposited with a range of magnetic ion concentrations to optimize both the Curie temperature and magnetization. The relationship between the atomic structure and magnetic properties will be determined and compared to theory. The highly accurate fully linearized augmented plane wave (FLAPW) method will be used for these calculations. Of specific interest is the extent to which magnetic ion clustering occurs and their role in the formation of alloys with high Curie temperatures. Experimental techniques to be used included high resolution transmission electron microscopy, extended x-ray fine structure analysis (EXAFS), temperature and field dependent magnetization measurements, Hall effect and magneto-optical measurements. Several thin film spintronic electronic and opto-electronic heterostructures will be fabricated and their spin dependent properties measured. The program will involve the training of both doctoral graduate and undergraduate students in magnetic semiconductor materials and device research. Collaborations between Sandia National Laboratories and Northwestern. University will be further developed. International collaboration with U. of Ulsan, South Korea will be undertaken.