Ferromagnetism in Semiconductors

[804313] Heiman：这项研究的目的是研究铁磁性半导体的合成，总体目标是发现在信息时代有用的新器件材料。该项目致力于高居里温度、铁磁性掺杂锰的砷化镓的合成和性能，它有可能表现出强磁性、电学和光学行为。硫族铕等磁性半导体是良好的磁体，但电学性能较差，光学性能有限，而掺杂锰的II-VI材料等稀磁性半导体具有较好的电学和光学性能，但磁性较弱。用MBE生长Gal-xMnxAs/Ga1-yAlyAs薄膜和量子阱。已知在GaAs中，Mn2+取代Ga3+会导致深度受体态。当孔浓度高于莫特准则（~2x1019 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交换产生了铁磁性。一个关键问题是如何控制材料中孔的数量。空穴浓度以及最终的居里温度取决于未知的类供体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。进一步的研究将解决纳米粒子量子点的自组装问题，以及为巨磁阻材料构建多层结构的可行性。该项目涉及具有高技术相关性的材料科学主题领域的基础研究问题。该研究将为电子/光子/磁性器件的重要方面提供基础材料科学知识。从研究中获得的基本知识和理解有望通过为设计和生产改进的材料和材料组合提供基本的理解和基础，从而有助于提高先进设备的性能。该计划的一个重要特点是通过培养学生在一个基础和技术上重要的领域的研究和教育的整合。

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.