We have studied magnetic semiconductor (Ga@sub 1-x@Mn@sub x@)As thin films and III-V based magnetic heterostructures, and present their molecular beam epitaxial growth, structure, magnetic, transport, and magnetooptic properties. The present work, we believe, will give new opportunities to explore an interdisciplinary field between semiconductors and magnetics. (Ga@sub 1-x@Mn@sub x@)As thin films were grown by low-temperature molecular-beam epitaxy (LT-MBE) at 200C - 300C on GaAs(001) substrates. Homogeneous ternary alloys with the Mn content x up to ~0.10 were obtained, and the lattice constants of the zinc-blende (GaMn)As are slightly larger (< 0.4 %) than that of GaAs.@footnote 1@ The (GaMn)As thin films showed a ferromagnetic order with the Curie temperature of 10 K - 100 K. Systematic study indicates that the ferromagnetism of GaMnAs is induced by carriers (holes). The concept of bandgap engineering is well established in nonmagnetic semiconductors. Here, we demonstrate the successful growth of III-V based superlattice (SL) structures consisting of ferromagnetic semiconductor (GaMn)As and nonmagnetic semiconductor AlAs.@footnote 2,3@ Both x-ray diffraction and transmission electron microscopy showed that the SLs are formed with excellent crystal quality and abrupt interfaces. Magnetooptic spectra of these SLs have revealed that, due to quantum confinement effect, the interband transition is systematically blue-shifted with decreasing the thickness of GaMnAs, and that some higher subbands are formed. Furthermore, we have fabricated GaMnAs/AlAs/GaMnAs ferromagnetic tunnel junctions, and have demonstrated large tunneling magnetoresistance (TMR). The feasibility of preparing such magnetic quantum heterostructures based on (GaMn)As, we believe, will open up unique possibility of coupling spinrelated phenomena with the well-established band engineering in III-V semiconductors.
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@footnote 1@ T. Hayashi, M. Tanaka, T. Nishinaga, H. Shimada, H. Tsuchiya, Y. Ootuka, 8th Int. Conf. on Molecular Beam Epitaxy, Malibu, August 1996, J. Cryst. Growth 175/176, 1063 (1997). @footnote 2@ T. Hayashi, M. Tanaka, K. Seto, T. Nishinaga, H. Shimada, K. Ando, Appl. Phys. Lett. 71, 1825 (1997). @footnote 3@ M. Tanaka, J. Vac. Sci. & Technol. B16, 2267(1998).