Spin coherence of electrons and its control in semiconductor quantum structures

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In this project, we carried out researches on (1) manifestation and control of spin coherence of electrons, (2) elucidation and control of interaction between electrons and nuclear spins or localized magnetic spins in semiconductor quantum structures, and (3) fabrication of novel devices which utilize spin-dependent electronic and optical properties based on the hybridization of conventional nonmagnetic semiconductor heterostructures and ferromagnetic semiconductors. During the term, we got the following results.1. We demonstrated, for the first time, the electric field control of ferromagnetism of a ferromagnetic semiconductor (In,Mn)As. Using a field effect transistor structure, we controlled the hole concentration in (In,Mn)As channel by a gate voltage so that the hole-mediated ferromagnetic interaction can be modulated.2. Using tow-temperature molecular beam epitaxy (LT-MBE), we successfully prepared zinc-blende CrSb, which does not exist in nature. We also demonstrated that the zi … More nc-blende CrSb is room-temperature ferromagnetic.3. We prepared (Ga,Mn)As/(Al,Ga)As/(Ga.Mn)As ferromagnetic semiconductor trilayer structures by LT-MBE in order to investigate spin-dependent transport properties. In such all semiconductor trilayer structures, we successfully demonstrated the giant magnetoresistance and tunnel magnetoresistance (TMR) effects, which have been widely utilized in magnetoelectronics devices made of metal-based junctions, in particular, exceeding 100% TMR has been realized in a (Ga,Mn)As/GaAs/(Ga,Mn)As tunnel junction.4. We prepared modulation doped GaAs/AlGaAs(110) quantum wells by MBE, and investigated the spin coherence time of electrons by a time-resolved Faraday rotation (TRFR) technique. We observed resonant spin amplification, which indicates that the electron spin coherence time is nearly 10 ns, and all optic unclear magnetic resonance.5. We prepared a spin Esaki diode, which consists of a p-(Ga,Mn)As/n-GaAs, and demonstrated electrical electron spin injection into a nonmagnetic semiconductor via interband spin tunneling in the structure. Less