CPM Seminar

Magneto-Optical Kerr Effect (MOKE) Studies of Spin Drift and Diffusion in n:GaAs Epilayers and Spin-Transport Devices

Madalina Furis

University of Vermont

Progress in miniaturization steadfastly leads us towards devices in which the quantum mechanical properties dominate the behavior of charge carriers in semiconductors. One such property, the electron spin, is exploited by the concept of “spintronics” or spin-based electronics, a radically new approach implying the transfer and storage of information through spin, rather than charge. Researchers envision the development of an entirely new class of devices, such as spin-LEDs (light emitting diodes) or spin- transistors, which combine the transport, optical and magnetic properties of electrons in semiconductors. The practical realization of such devices implies a means to inject, detect and manipulate spin-polarized electrons in semiconductors.

I will show how scanning Kerr microscopy is employed in order to locally probe and spatially resolve[1] the drift and diffusion of spin polarized electrons in n:GaAs epilayers and Fe/GaAs lateral spin transport devices. These measurements map out[2] the injection of spin-polarized electrons from a source contact into a lateral GaAs channel and the accumulation of spin-polarized electrons near the drain contact. The direction of the spin-polarized electrons momentum k is determined by exploiting symmetries of the effective magnetic fields, which arise from strain-induced spin-orbit coupling in GaAs. Depolarization of electron spin distribution by transverse magnetic fields (Hanle effect curves provides a measure of the spin lifetime[3] and spin transport parameters such as drift velocity or mobility.

[1] Local Hanle-effect studies of spin drift and diffusion in n:GaAs epilayers and spin-transport devices (invited paper), M. Furis, D. L. Smith, S. Kos, E. S. Garlid, K. S. M. Reddy, C. J. Palmstr�m, P. A. Crowell, and S. A. Crooker , New Journal of Physics, in print.
[2] Imaging the injection and accumulation of spin-polarized electrons in lateral ferromagnet/semiconductor devices S. A. Crooker, M. Furis, X. Lou, C. Adelmann, D. L. Smith, C. J. Palmstr�m, and P. A. Crowell, Science 309, 2191 (2005)
[3] Bias-dependent electron spin lifetimes in n-GaAs and the role of donor impact ionization, M. Furis, D. L. Smith, S. A. Crooker, and J. L. Reno, Applied Physics Letters 89, 102102 (2006)