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Injection de spin dans le germanium : de l'injecteur ferromagnétique métallique à l'injecteur semiconducteur (Ge,Mn)

Abstract : Creation of spin polarization in non-magnetic semiconductors is one of the prerequisite for creation of spintronics based semiconductor devices. Germanium is interesting for spintronics applications due to its high carrier mobilities and its inversion symmetry that gives long spin lifetimes. In this manuscript, we discuss two approaches for electrical spin injection and detection in Germanium. The first approach is to use a tunnel barrier and a ferromagnetic metal as a spin injector. The tunnel barrier at the interface circumvents the conductivity mismatch problem. Two different spin injectors are used: Py/Al2O3 and CoFeB/MgO. The measurements are performed in three-terminal geometry and the proof of spin accumulation is given by Hanle measurements. In case of Al2O3, the spin accumulation is predicted to be in localized states at the oxide/Ge interface and the spin signal is observed up to 220 K. However in MgO based devices, true injection in Ge channel is predicted and spin signal of 20-30 µV is observed at room temperature. The second approach of using ferromagnetic semiconductor (Ge,Mn) as spin injector is also discussed. The structural and magnetic properties of (Ge,Mn) thin-films grown by low-temperature molecular beam epitaxy (LT-MBE) are studied. Depending on the growth parameters, crystalline/amorphous GeMn nanocolumns and Ge3Mn5 thin films or nanoclusters have been observed. Magnetic anisotropy in these nanostructures is also studied. Finally, the growth of (Ge,Mn) films on GOI substrates is shown and different ways to use (Ge,Mn) as a spin injector in Ge are discussed to achieve all-semiconductor based spintronics devices.
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Abhinav Jain. Injection de spin dans le germanium : de l'injecteur ferromagnétique métallique à l'injecteur semiconducteur (Ge,Mn). Autre [cond-mat.other]. Université de Grenoble, 2011. Français. ⟨NNT : 2011GRENY049⟩. ⟨tel-00647310⟩

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