OHNO Yuzo Research Institute of Electrical Communication, Tohoku University, Research Associate, 電気通信研究所, 助手 (00282012)
MATSUKURA Fumihiro Research Institute of Electrical Communication, Tohoku University, Research Associate, 電気通信研究所, 助手 (50261574)
|Budget Amount *help
¥13,700,000 (Direct Cost: ¥13,700,000)
Fiscal Year 1999: ¥5,400,000 (Direct Cost: ¥5,400,000)
Fiscal Year 1998: ¥8,300,000 (Direct Cost: ¥8,300,000)
III-V semiconductors and/or diluted magnetic semiconductors, and their nanostructures were grown by low-temperature (LT-) molecular beam epitaxy (MBE). The growth dynamics and structures have been investigated by reflection high energy electron diffraction (RHEED), and atomic force (AFM) and/or magnetic force (MFM) microscopy. Their optical, magnetic, and transport properties of the samples were also characterized.
The summary of the research results are :
1. It has been observed that the oscillation of the RHEED intensity recovers as the growth temperature was much lowered (〜300℃). The experimental results of the temperature dependence were successfully represented by Monte-Carlo simulation calculation based on the model which treats the excess arsenic as self-surfactant.
2. A new diluted magnetic semiconductor (Ga,Mn)Sb with a few percent Mn concentration has been successfully grown by MBE. The dependence of their properties on the growth temperature was investigated by AFM/MFM, magneti
zation and magnetotransport measurements. By AFM and MFM observations, it was found that MnSb clusters were formed on the surface. When the growth temperature is as high as 〜560℃, the sample is ferromagnetic at room temperature, and the MnSb clusters dominate the whole magnetization properties. On the other hand, the magnetization and magnetotransport properties of the samples grown at LT exhibit another magnetic phase below 20 K, indicating the existence of (Ga,Mn)As which becomes ferromagnetic at lower temperatures (〜20 K).
3. It has been demonstrated that size uniformity of the self-assembled InMnAs quantum dots grown on (211)B GaAs substrate can be improved by introducing Mn, indicating that Mn plays a role of surfactant.
4. All-semiconductor ferromagnet (GaMn)As/nonmagnet (Al,Ga)As/ferromagnet (Ga,Mn)As trilayer structures were fabricated by LT-MBE, and their magnetic and transport properties were characterized. It has been demonstrated that the magnetic coupling between two ferromagnetic layers can be controlled by tuning the thickness and/or the barrier hight of the non-magnetic layer. Furthermore, we have observed the giant magnetoresistance effect in this system for the first time. Less