Ferromagnetism in Semiconductors

9804313 Heiman本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GaAs掺杂Mn的合成和性能，它有可能表现出强磁性以及电学和光学行为。磁性半导体如铕硫属化物是良好的磁体，但具有差的电性能和有限的光学性能，而稀磁性半导体如锰掺杂的II-VI族材料显示出更好的电性能和光学性能，但弱磁性。用分子束外延法生长Ga_xMn_xAs/Ga_（1-y）Al_yAs薄膜和量子威尔斯。Mn ~（2+）取代GaAs中的Ga ~（3+）导致深受主态。当空穴浓度高于Mott标准（~ 2x 1019 cm-2）时，产生金属态。据信，磁性Mn 2+离子和空穴之间的强p-d交换产生铁磁性。关键问题是如何控制材料中的孔的数量。空穴浓度，最终居里温度，取决于未知的施主类状态的补偿程度的空穴。锰和空穴浓度的适当控制预计会导致居里温度的增加。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。 该项目解决了具有高技术相关性的材料科学专题领域的基础研究问题。该研究将在基础层面上为电子/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预计将有助于提高先进设备的性能，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。 该计划的一个重要特点是通过在一个基本和技术上重要的领域对学生进行培训来整合研究和教育。

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.