Growth and properties of III-V-semiconductor/ferromagnet hybrid materials system (GaAs : Mn)

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Recent progress in epitaxial growth technology has made it possible to prepare a variety of new artificial thin films and heterostructures (HSs) consisting of dissimilar materials. Among them, stable epitaxial ferromagnet/semiconductor HSs offer unprecedented opportunities for basic and applied research, adding a new degree of freedom in materials design. We have studied epitaxial growth and physical properties of such novel dissimilar heterostructures focusing on ferromagnetic compound/Ill-V semiconductor systems.We have successfully grown MnAs/GaAs(00l) and MnAs/Si(001) ferromagnet/semiconductor single HSs, and MnAs/GaAs/MnAs ferromagnet/semiconductor trilayer HSs on GaAs (111)B and on Si(111) substrates by molecular-beam epitaxy (MBE). Despite dissimilarity in crystal structure, chemical bonding, electronic and magnetic properties, cross-sectional images by transmission electron microscopy showed that the HSs are formed as intended with fairly smooth and atomically abrupt interfaces. In the trilayer HSs, double-step features were observed in magnetization characteristics due to the difference in coercive force between the top and bottom MnAs layers. The interlayer coupling was little when the thickness of the GaAs spacer layer was 5-10 nm.We have also studied epitaxial growth and properties of (GaMn)As thin films and (GaMn)As/A1As quantum HSs grown by low-temperature MBE.(GaMn)As is a new class of III-V based magnetic alloy semiconductor, which contains a large amount of Mn atoms (up to -8%) far above the equilibrium solubility limit of Mn in GaAs. We show that the feasibility of preparing such a III-V based ferromagnetic semiconductor and its HSs gives a new degree of freedom in the materials design of III-V systems, as well as device applications using both magnetic and optical/electronic functions in III-V semiconductors.