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

研究了从铁磁体向半导体注入自旋，并验证了自旋注入的高效率。我们还证实了基于自旋注入技术的自旋晶体管在Fe/InAs杂化结构中的工作。分项研究结果列于下表。(1) Fe/InAs自旋二极管的电致发光圆极化测量表明，圆极化度可达18-20%，自旋注入效率可达36-40%。(2)利用次级离子质谱（SIMS）、透射电子显微镜（TEM）和反射高能电子衍射（RHEED）研究了在23℃和175℃条件下生长的MBE样品在Fe/InAs界面上的表面反应。175℃试样界面处存在交叉扩散，23℃试样界面处无交叉扩散。透射电镜显示，两种样品在大部分区域存在原子突变界面。虽然在一些地方观察到一层或两层结构不明的单原子层，但界面反应不是很清楚。RHEED研究表明，在23℃试样中，铁生长初期形成较多的岛状铁。低温生长可以保持良好的界面，从而获得更好的发光和自旋注入性能。(3)基于Fe/InAs混合体系的基本自旋注入研究，通过观察与InP衬底相匹配的InAlAs势垒层包覆的高铟含量InGaAs沟道中栅极控制电流振荡，证实了自旋晶体管的工作。这是对自旋晶体管工作的首次观察。

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.