Regensburg 2002 – wissenschaftliches Programm

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SYSP: Spintronics in Grundlagen und Anwendungen


SYSP II.1: Hauptvortrag

Donnerstag, 14. März 2002, 10:00–10:30, H1

Electrical spin injection from ferromagnetic metals into GaAs — •Manfred Ramsteiner, Haijun Zhu, Atsushi Kawaharazuka, Hsin-Yi Hao, and Klaus H. Ploog — Paul Drude Institute for Solid State Electronics, Hausvogteiplatz 5-7, 10117 Berlin, Germany

Spintronic semiconductor devices utilize not only the charge, but also the spin of electrons to achieve novel functionalities. The realization of such devices relies on the ability to inject a spin-polarized current into a semiconductor (SC). In principle, the ferromagnetic metals (FM) Fe and MnAs are excellent candidates for spin injection at room temperature. However, prior to our work, spin injection from a FM into a SC was regarded to be impossible.

We present experimental evidence that spin injection from the ferromagnetic metals Fe and MnAs into the semiconductor GaAs is indeed possible. The spin polarization of injected electrons is detected by the circular polarization degree P of the electroluminescence (EL) from n-i-p (In,Ga)As/GaAs light emitting diodes containing FM injection layers.

As a proof for spin injection, we require that the polarization degree P as a function of an external magnetic field follows the out-of-plane magnetization curves of the FM injection layers. Indeed, our measured EL polarization curves fulfill this requirement over the whole magnetic field range for both Fe and MnAs injection layers. If the spin relaxation time τS in the quantum wells is comparable or considerably shorter than the recombination lifetime τR, the measured value of P is a lower limit for the spin injection efficiency η=(1 + τR / τS) × P. From time-resolved measurements it turns out, that our data correspond to an spin injection efficency of about 5% for Fe/GaAs at room temperature.

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