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

外延生长技术的最新进展使得制备各种新型的人工薄膜和异质结构（HS）成为可能。其中，稳定的外延铁磁体/半导体HS为基础和应用研究提供了前所未有的机会，为材料设计增加了新的自由度。我们以铁磁化合物/Ⅲ-Ⅴ族半导体系统为研究对象，采用分子束外延（MBE）技术在GaAs（111）B和Si（111）衬底上成功地生长了MnAs/GaAs（001）和MnAs/Si（001）铁磁/半导体单层HS和MnAs/GaAs/MnAs铁磁/半导体三层HS。尽管在晶体结构，化学键，电子和磁性的不同，通过透射电子显微镜的横截面图像显示，HS形成预期的相当光滑和原子突变的界面。在三层HS中，由于顶部和底部MnAs层之间的矫顽力差异，在磁化特性中观察到双台阶特征。GaAs间隔层厚度为5-10 nm时，层间耦合很小。我们还研究了低温MBE外延生长的（GaMn）As薄膜和（GaMn）As/Al As量子HS的外延生长和性质。（GaMn）As是一种新型的III-V族磁性合金半导体，其Mn原子含量高达~ 8%，远远超过了Mn在GaAs中的平衡溶解度极限。我们表明，这种III-V基铁磁半导体及其HSs的制备的可行性提供了一个新的自由度的III-V系统的材料设计，以及使用III-V半导体的磁性和光学/电子功能的设备应用。

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.