Abstract
Group-IV-based ferromagnetic semiconductor Ge1−xFex (GeFe) is one of the most promising materials for spin injection/detection in Si and Ge. In this paper, we demonstrate a systematic study of tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) composed of Fe/MgO/Ge1−xFex with various Fe concentrations (x = 0.065, 0.105, 0.140, and 0.175). With increasing x, the TMR ratio increases up to 1.5% when x≤ 0.105, and it decreases when x> 0.105. This is the first observation of the TMR ratio over 1% in MTJs containing a group-IV ferromagnetic semiconductor. With increasing x, while the Curie temperature of GeFe increases, the MgO surface becomes rougher, which is thought to be the cause of the upper limit of the TMR ratio. The quality of the MgO layer on GeFe is an important factor for further improvement of TMR in Fe/MgO/GeFe MTJs.
Highlights
Exploiting the spin dependent transport in group-IV semiconductors is important for future semiconductor-based spintronics
Ge1 xFex (GeFe) is one of the most attractive materials for efficient spin injection/detection in Si and Ge1,2 because GeFe can be epitaxially grown on Si and Ge substrates by low temperature molecular beam epitaxy (LT-MBE) and its conductivity can be varied from metallic to insulating by boron (B) doping
Considering the recent first-principles calculations, which estimated the spin polarization of GeFe to be 70%,7 the tunneling magnetoresistance (TMR) ratio is expected to be enhanced to 270% in Fe/MgO/GeFe [here, the effective spin polarization of Fe(/MgO) is considered to be 75%]
Summary
Exploiting the spin dependent transport in group-IV semiconductors is important for future semiconductor-based spintronics. By decreasing the mesa size and by increasing x, we successfully increase the TMR ratio up to 1.5%.
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