Thin Film Diluted Magnetic Semiconductors with Tetradymite Structure

本项目探讨了四钇型A2V B3VI （A=Bi, Sb； B=Te, Se）半导体家族中电子自由度和自旋自由度的同时存在。通过这些材料的薄膜，人们寻求在四钛矿型半导体中掺入相对高浓度的磁性杂质，从而获得更高的居里温度。该项目侧重于几个目标：1)证明掺杂过渡金属的Sb2Te3、Bi2Te3和Bi2Se3薄膜的生长，以及这些二元化合物的合金和超晶格；2)探索磁性杂质在这些寄主中的结合上限（相图）；3)对所获得的DMS（稀磁性半导体）薄膜的结构、磁性和输运特性进行全面的表征。利用电导率、磁阻、热功率、导热系数、比热、霍尔效应、磁化、该项目预计将推进稀释磁性半导体的基础知识，从而为未来的自旋电子学应用奠定基础。由于晶体结构和所提出材料中使用的磁性离子与传统的稀释磁性半导体（如mn掺杂的III-V或II-VI化合物）明显不同，该项目可能会对半导体中的磁性基本问题，甚至可能是磁性的基本问题有新的认识。四白石型晶体结构的高各向异性环境及其明显的原子八面体配位可能对磁序的形成起关键作用；这与锰掺杂锌闪锌矿或纤锌矿结构的立方体环境形成鲜明对比，它们具有独特的四面体键合。本项目研究材料科学中与技术相关的主题领域的基础材料和凝聚态物理研究问题，并强调研究与教育的整合。研究生和本科生将参与电子/磁性材料的合成、加工和表征。在MBE增长、半导体物理和磁学领域对研究生和本科生进行培训，为他们提供了研究和教育的特殊机会，并为未来的劳动力提供了良好的投资。该项目由DMR电子材料和凝聚态物理项目共同支持

This project explores the simultaneous presence of electronic and spin degrees of freedom in the tetradymite-type A2V B3VI (A=Bi, Sb; B=Te, Se) family of semiconductors. The incorporation of relatively high concentrations of magnetic impurities in tetradymite-type semiconductors, and thus higher Curie temperatures, is sought through thin films of these materials. The project focuses on several objectives: 1) to demonstrate the growth of thin films of Sb2Te3, Bi2Te3, and Bi2Se3 -as well as alloys and superlattices of these binary compounds-doped with transition metals; 2) to explore the upper limits of incorporation of the magnetic impurities (phase diagram) in these hosts; and 3) pursue a comprehensive program of characterization of the structural, magnetic, and transport properties of the obtained DMS (dilute magnetic semiconductor) films. The role of the magnetic impurities in the tetradymite semiconductors and their impact on properties will be studied employing electrical conductivity, magnetoresistance, thermopower, thermal conductivity, specific heat, Hall effect, magnetization, and magnetic susceptibility measurements from temperatures of 2K to 300K and in magnetic fields of 0 to 9 T. The project is expected to advance basic knowledge of diluted magnetic semiconductors and thereby help lay groundwork for future spintronics applications. Since the crystal structure and the magnetic ions utilized in the proposed materials are distinctly different from traditional diluted magnetic semiconductors such as Mn-doped III-V or II-VI compounds, the project may shed new light on fundamental issues of magnetism in semiconductors, and possibly of magnetism generally. The highly anisotropic environment of the tetradymite-type crystal structure with its pronounced octahedral coordination of atoms may play a key role in the development of magnetic order; this is in contrast to the cubic environment of Mn-doped zinc-blende or wurtzite structures with their distinct tetrahedral bonding.%%% This project addresses basic materials and condensed matter physics research issues in a topical area of materials science with technological relevance, and places emphasis on the integration of research and education. Graduate and undergraduate students will be involved in the synthesis, processing, and characterization of electronic/magnetic materials. Training of graduate and undergraduate students in the areas of MBE growth, semiconductor physics, and magnetism provides special opportunities for them in research and education, and a sound investment in the future workforce. The project is jointly supported by the DMR Electronic Materials and Condensed Matter Physics programs.***