Ferromagnetism in Semiconductors

9804313海曼，这项研究的目的是研究铁磁性半导体的合成，总的目标是发现在信息时代有用的新器件材料。该项目研究了掺锰的高居里温度铁磁性砷化镓的合成和性质，它具有很强的磁性以及良好的电学和光学性能。Eu硫化物等磁性半导体是很好的磁体，但电学性能较差，光学性能有限，而掺锰II-VI材料等稀磁半导体显示出较好的电学和光学性能，但磁性较弱。采用分子束外延技术生长了Ga1-xMnxAs/Ga1-yAlyAs薄膜和量子阱。众所周知，在GaAs中，Mn2+取代Ga3+会导致较深的受主能级。当空穴浓度高于Mott准则(~2×1019 cm-2)时，产生金属态。人们认为磁性Mn2+离子与空穴之间的强p-d交换会产生铁磁性。一个关键问题是如何控制材料上的孔洞数量。空穴浓度以及最终的居里温度取决于未知施主类态对空穴的补偿程度。适当控制锰和空穴浓度有望导致居里温度升高。进一步的研究将涉及MNAs量子点的自组装，以及构建巨磁电阻材料多层结构的可行性。%该项目致力于具有高度技术相关性的材料科学主题领域的基础研究问题。这项研究将在基础水平上为电子/光子/磁性设备的重要方面贡献基本的材料科学知识。从研究中获得的基本知识和理解有望为改进材料和材料组合的设计和生产提供基本的了解和依据，从而有助于提高先进器件的性能。该计划的一个重要特点是通过在一个具有根本意义和技术意义的领域对学生进行培训，将研究和教育结合起来。

9804313 Heiman The aim of this research is to investigate the synthesis of semiconductors that are ferromagnetic the overall goal is to discover new device materials useful in the information age. The project addresses the synthesis and properties of high-Curie- temperature, ferromagnetic GaAs doped with Mn, which has the potential to exhibit strong magnetic as well as electrical and optical behavior. Magnetic semiconductors such as the europium chalcogenides are good magnets but have poor electrical properties and limited optical properties, while dilute magnetic semiconductors such as manganese-doped II-VI materials show better electrical and optical properties but weak magnetism. Thin films and quantum wells of Gal-xMnxAs/Ga1-yAlyAs will be grown by MBE. It is known that Mn2+ substituting for Ga3+ in GaAs leads to deep acceptor states. When the hole concentration is above the Mott criterion (~2x1019 cm-2) a metallic state is produced. It is believed that a strong p-d exchange between the magnetic Mn2+ ions and holes generates ferromagnetism. A key issue is how to control the number of holes in the material. The hole concentration, and ultimately the Curie temperature, depend on the degree of compensation of the holes by unknown donor-like states. Proper control of the manganese and hole concentration is expected to lead to increased Curie temperatures. Further investigations will address the self-assembly of MnAs quantum dots, and the feasibility of building multilayer structures for giant magnetoresistance materials. %%% The project addresses basic research issues in a topical area of materials science having high technological relevance. The research will contribute basic materials science knowledge at a fundamental level to important aspects of electronic/photonic/magnetic devices. The basic knowledge and understanding gained from the research is expected to contribute to improving the performance of advanced devices by providing a fundamental understan ding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area.