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

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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.