Regensburg 2000 – scientific programme

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HL: Halbleiterphysik

HL 41: Symposium: Spin-dependent transport in semiconductors - towards a spin transistor

HL 41.3: Fachvortrag

Friday, March 31, 2000, 11:40–12:05, H15

Electrical spin-injection into semiconductors - From Cobalt contacts to semiconductor spin-aligners — •Georg Schmidt and Laurens W. Molenkamp — Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg

During the past years intensive research efforts were dedicated to spin-injection using ferromagnetic metal contacts on a semiconductor two dimensional electron gas. Although different material systems have been explored, all results published so far show small effects close to the detection limit which may as well originate from stray Hall-voltages or magnetoresistance. An explanation for this lack of success is offered by a simple thermodynamic model for a diffusive metal-semiconductor device. The model indicates that in the linear response regime, experiments using ferromagnetic metal-contacts for spin-injection into a semiconductor will not yield detectable changes in device resistance. However, these problems may be circumvented by using a spin-injector with 100% spin-polarization.

We have experimentally demonstrated such an injector, utilizing a semimagnetic semiconductor as a spin-aligner. We have fabricated a GaAs/AlGaAs-LED with a ZnBeMnSe spin-aligner contact, which allows for efficient injection of spin-polarized electrons into the GaAs. The spin-polarization of the current may be detected via the circular polarization of the LED’s electroluminescence and is up to 90%. Faraday effect and giant magnetic circular dichroism as a possible origin of the polarization could be ruled out.