Thin Film Diluted Magnetic Semiconductors with Tetradymite Structure

这个项目探索了四氯化钛类型的A2V B3VI(A=Bi，Sb；B=Te，Se)半导体家族中电子和自旋自由度的同时存在。人们通过这种材料的薄膜来寻求在辉钛矿型半导体中加入相对高浓度的磁性杂质，从而获得更高的居里温度。该项目集中于几个目标：1)展示Sb2Te3、Bi2Te3和Bi2Se3-以及这些二元化合物的合金和超晶格的生长-掺杂过渡金属；2)探索磁性杂质(相图)在这些基质中的掺杂上限；以及3)对所获得的DMS(稀磁半导体)薄膜的结构、磁性和输运性质进行全面的表征。该项目将通过在2K到300K的温度和0到9T的磁场中的电导率、磁阻、热电势、热导率、比热、霍尔效应、磁化强度和磁化率的测量来研究磁性杂质在四氯化钛半导体中的作用及其对性能的影响。该项目有望增进稀磁半导体的基本知识，从而为未来的自旋电子学应用奠定基础。由于该材料的晶体结构和使用的磁性离子与传统的稀磁半导体(如掺锰的III-V或II-VI化合物)截然不同，该项目可能会为半导体中的磁性基本问题，甚至可能是一般磁性问题提供新的线索。具有显著八面体原子配位的四方闪锌矿晶体结构的高度各向异性环境可能在磁性秩序的发展中起关键作用；这与具有明显四面体成键的掺锰闪锌矿或纤锌矿结构的立方环境形成对比。%本项目致力于基础材料和凝聚态物理研究，该领域是与技术相关的材料科学的热门领域，强调研究和教育的结合。研究生和本科生将参与电子/磁性材料的合成、加工和表征。在分子束外延增长、半导体物理和磁学领域对研究生和本科生的培训为他们在研究和教育方面提供了特殊的机会，并对未来的劳动力进行了稳健的投资。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.***