Spin coherence of electrons and its control in semiconductor quantum structures

在这个项目中，我们开展了以下方面的研究：(1)电子自旋相干性的表现和控制；(2)半导体量子结构中电子与核自旋或局域磁自旋相互作用的阐明和控制；(3)基于传统的非磁性半导体异质结和铁磁半导体的杂化，利用自旋相关的电子和光学性质的新型器件的制备。在这一学期里，我们取得了以下成果。我们首次证明了铁磁半导体(In，Mn)As铁磁性的电场控制。我们使用场效应晶体管结构，通过栅极电压控制(In，Mn)As沟道中的空穴浓度，从而可以调制空穴介导的铁磁相互作用。利用双温分子束外延(LT-MBE)技术，成功地制备了自然界中不存在的闪锌矿CrSb。我们还演示了zi…更多的NC-闪锌矿CrSb具有室温铁磁性。为了研究自旋相关的输运性质，我们用LT-MBE方法制备了(Ga，Mn)As/(Al，Ga)As/(Ga.Mn)As铁磁半导体三层结构。在这种半导体三层结构中，我们成功地展示了巨磁电阻效应和隧道磁阻效应，这两种效应已经被广泛应用于金属基结的磁电子器件中，特别是在a(Ga，Mn)As/GaAs/(Ga，Mn)As隧道结中实现了超过100%的TMR。我们用分子束外延技术制备了调制掺杂的GaAs/AlGaAs(110)量子阱，并用时间分辨法拉第旋转(TRFR)技术研究了电子的自旋相干时间。我们观察到了共振自旋放大，这表明电子自旋相干时间接近10 ns，并且全光不清楚核磁共振。我们制备了由p-(Ga，Mn)As/n-GaAs组成的自旋Esaki二极管，并通过带间自旋隧道效应将电子自旋注入到非磁性半导体中。较少

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