Fabrication of Semiconductor Spin Device -Integration of Spin Transistor and Quantum Dots -

研究了铁磁体对半导体的自旋注入，验证了高效率自旋注入。我们也证实了在Fe/InAs杂化结构中基于自旋注入技术的自旋晶体管工作。具体研究结果如下：(1)对Fe/InAs自旋二极管的电致发光进行了圆极化测量，发现其圆极化程度为18-20%，自旋注入效率为36-40%。(2)用二次离子质谱仪、透射电子显微镜和反射高能电子衍射仪研究了分子束外延生长过程中Fe/InAs界面的表面反应，比较了在23℃和175℃下生长的样品。在175℃样品中观察到界面上的交叉扩散，而在23℃样品中没有观察到交叉扩散。透射电子显微镜显示，在这两个样品中，大部分区域的界面是原子突变的。虽然在一些地方观察到了一到两个未知结构的单原子层，但界面反应并不是很清楚。RHEED研究表明，在Fe生长的初始阶段，23℃样品中有更多的Fe岛形成。在Fe/InAs混合系统中的基本自旋注入研究的基础上，通过观察与InP衬底匹配的InAlAs势垒层覆盖的高InIn含量InGaAs沟道中的栅控电流振荡，证实了自旋晶体管的工作。这是第一次观察到自旋晶体管的工作原理。

Spin injection from ferromagnet into semiconductor has been investigated and high efficiency spin injection was verified. We have also confirmed the spin transistor operation based on the spin injection technique in Fe/InAs hybrid structure. Itemized research results are listed below.(1)Circular polarization measurements of electroluminescence from Fe/InAs spin diode revealed that the degree of circular polarization of 18-20% and spin injection efficiency of 36-40% is possible.(2)Surface reaction at the Fe/InAs interface has been investigated using Secondary Ion Mass Spectroscopy (SIMS), Transmission Electron Microscopy (TEM) and Reflection High Energy Electron Diffraction (RHEED) during the MBE growth comparing two samples grown at 23℃ and at 175℃. Cross diffusion was observed at the interface in 175℃ sample but not in 23℃ sample. TEM showed atomically abrupt interface in both samples in large part of the region. Although one or two mono-atomic layers of unknown structure were observed in some places, interface reaction was not so clear. RHEED study revealed more island formation of Fe at the initial stage of the Fe growth in 23℃ sample. Lower temperature growth was shown to maintain better interface for better luminescence and spin injection properties.(3)Based on the basic spin injection study in Fe/InAs hybrid system, we have confirmed the spin transistor operation by observing the gate controlled current oscillation in high indiun content InGaAs channel clad by InAlAs barrier layers lattice matched to InP substrate. This is the first observation of spin transistor operation.