Study of Diffusion of Magnetic Ions in Semiconductor Heterostructures and Its Effect on Spin Injection

技术：目前研究的许多自旋电子器件涉及从铁磁材料到非磁性半导体的自旋注入。最近的研究表明，当含Mn和Fe的铁磁性金属在GaAs或Si上生长时，会发生显著的扩散。最近也有报道表明，在自旋极化载流子注入非磁性结构后，存在自旋散射的证据。因此，对这一问题进行系统的研究，以提高对注入结果的分析水平，具有重要的意义。本项目主要研究磁性离子在Fe/GaAs、FeCo/GaAs、MNAs/GaAs和GaMnAs/GaAs等最常用的体系中的扩散，以及一些涉及硅的结构。样品采用分子束外延生长。用飞行时间二次离子质谱仪和横截面扫描隧道显微镜测定了扩散分布。扩散的磁性离子对自旋注入的影响主要取决于自旋发光二极管结构，这在确定注入电子的自旋极化水平方面是有效的。这项研究旨在提供有关非磁性半导体中扩散的磁性离子的分布及其对自旋注入的影响的定量信息。通过研究扩散作为温度的函数通过退火，人们能够设置生长和器件加工温度的上限。该项目还探索了抑制磁性离子扩散过程的可能性。非技术性：这项科学工作可能对未来几代信息技术的发展产生重大影响。它解决了大多数自旋效应研究中存在的一个共同问题，即自旋极化电流从一种材料到另一种材料的传输。这将包括对自旋发光二极管、自旋激光、自旋阀和其他涉及铁磁材料的更复杂的自旋逻辑器件的研究。该项目还为培训下一代科学家做出了贡献，增加了另一个场所，为三名研究人员提供跨学科培训，这三名研究人员长期以来一直联合为研究生提供物理和化学方面的建议。此外，该项目还与布法罗的美洲原住民磁力学校(K-8)进行了接触，并在早期阶段让美洲原住民和非洲裔美国学生学习科学和工程。

Technical: Many currently studied spintronics devices involve spin injection from ferromagnetic materials into nonmagnetic semiconductors. Recent studies show that significant diffusion occurs when Mn and Fe containing ferromagnetic metals are grown on GaAs or Si. There are also recent reports showing evidence of spin scattering after spin-polarized carriers are injected into nonmagnetic structures. It is therefore important to investigate this problem systematically, so that the analysis of injection results can be improved. This project focuses on diffusion of magnetic ions in the most studied systems, namely Fe/GaAs, FeCo/GaAs, MnAs/GaAs and GaMnAs/GaAs, and on selected structures involving silicon. The samples are grown by molecular beam epitaxy. Diffusion profiles are determined using time-of-flight second ion mass spectroscopy and cross sectional scanning tunneling microscopy. The effect of diffused magnetic ions on spin injection is primarily determined with spin light emitting diode structures, which have been effective in determining the level of spin polarization of the injected electrons. The study is designed to provide quantitative information concerning the profile of diffused magnetic ions in nonmagnetic semiconductors, and their effect on spin injection. By examining diffusion as a function of temperature through annealing, one is able to put upper limits on growth and device processing temperatures. The project also explores the possibility of suppressing diffusion processes for the magnetic ions.Non-technical: This scientific work could have a significant impact on the development of future generations of information technology. It addresses a common issue that exists in most studies of spin effects involving transport of spin polarized currents from one material to another. This would include studies of spin light emitting diodes, spin lasers, spin valves and other more complicated spin-logic devices that involve ferromagnetic materials. The project also contributes to training the next generation of scientists by adding another venue to provide interdisciplinary training to students for the three investigators who have a long history of jointly advising graduate students in physics and chemistry. In addition, the project involves outreach to the Native American Magnet School (K-8) in Buffalo and engages, at an early stage, Native American and African American students in sciences and engineering.