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Theses

Electrical and optical detections of spin-filter effects in the ferromagnetic metal / semiconductor junctions

Abstract : The objective of this thesis work is to experimentally investigate the phenomena of the spin-dependent transport of hot electrons at room temperature into ferromagnetic metal (Fe or Co) / semiconductor (GaAs) Schottky junctions. In practice, a spin-polarized electron beam generated by optical orientation is injected into the two-terminal structure with energies varying from 10 to 3 keV above the Fermi level. The transmitted current shows a spin asymmetry, which depends on the relative orientation between the metal magnetization and the incident spin direction. In this PhD work, we have pursued two experimental approaches, one optical and the other electrical for detecting the transmitted current through the junction above the Fermi level, both exploiting the multiplication of electrons due to the generation of secondary electrons inside the metal layer. The electrical measurement requires of working with structures having a very high dynamic resistance of junction (typically a few M). The spin-dependent asymmetries are studied in samples characterized by different thicknesses of the oxide layer between magnetic metal layer and GaAs. We observe different transport regimes associated with the electron transmission at different interfaces. The optical measurement of the transmitted current is based on the radiative recombination of the injected electrons with the holes through the p-type semiconductor band gap. For this purpose a new structure including InGaAs quantum wells and one single Fe layer has been grown. Spin-polarized electrons injected into such a structure produce an asymmetry in the recombination light intensity. The variation of the luminescence asymmetry is studied relative the energy of the incident electrons. The optical detection offers the advantage of being less sensitive to the junction resistance.
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Contributor : Xiaoxin Li <>
Submitted on : Monday, November 7, 2011 - 6:02:08 PM
Last modification on : Wednesday, March 27, 2019 - 4:18:02 PM
Long-term archiving on: : Wednesday, February 8, 2012 - 2:36:05 AM

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  • HAL Id : pastel-00638986, version 1

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Xiaoxin Li. Electrical and optical detections of spin-filter effects in the ferromagnetic metal / semiconductor junctions. Materials Science [cond-mat.mtrl-sci]. Ecole Polytechnique X, 2011. English. ⟨pastel-00638986⟩

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