Microstructural evolution of epitaxial Fe/MgO layers grown on InAs(001) substrates

Microstructural evolution of epitaxial Fe/MgO layers grown on InAs(001) substrates
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Interest in the heterostructure of Fe/MgO/InAs is growing for spin-based electronic device applications due to the spin injection into a narrow gap semiconductor of high electron mobility and strong spin-orbit interaction (SOI) [1]. In addition, the MgO plays important roles of the elimination of conductivity mismatch as well as the enhancement of spin injection efficiency [2]. Here, we have systematically evaluated the crystal structure and morphology changes of the epitaxial Fe/MgO layers grown on InAs (001) substrates. The heterostructures of Fe/MgO/InAs are fabricated by using a cluster molecular beam epitaxy (MBE) system composed of two MBEs and a magnetron sputter interconnected through an ultra high vacuum (UHV) tube. The growth temperature of the MgO layer is used as a key experimental parameter ranged from room temperature to 400 °C. Cross-sectional high resolution transmission electron microscopy (HRTEM) observations reveal that the crystalline quality of the MgO layers is greatly enhanced as the growth temperature of increases. The subsequent Fe also shows the slight enhancement on the MgO layers grown at higher temperatures in spite of the identical Fe growth temperature of 200 °C. It is surprising that the three-dimensional (3D) Fe islands of less crystallinity are formed on the MgO layers grown at low temperatures due to a large lattice mismatch of 7.7% between MgO and InAs. However, the formation of the Fe islands is suppressed to the two-dimensional (2D) Fe layers on the MgO layers grown at high temperatures due to the partial strain relaxation of the underlying MgO layers. As a result, the inplane epitaxial relationship of Fe[010]//MgO[1-10]//InAs[1-10] is strongly improved with the better crystallinities of both Fe and MgO. The experimental results obtained in this study evidently point out that the MgO growth temperature is one of the most important factors determining the ...
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