Carrier induced ferromagnetism and its control in III-V diluted magnetic semiconductors

本研究的目的是阐明磁性与载流子浓度等半导体性质之间的关系，并探索利用III-V基稀释磁性半导体量子结构通过控制载流子浓度来控制磁性的可能性。在这里，我们主要集中在（Ga, Mn） As上，我们已经证明了它可以通过低温分子束外延生长，并且在低温下表现出空穴诱导的铁磁秩序。结果总结如下：1。通过磁输运测量，确定了（Ga, Mn） As的铁磁转变温度（T_c）和空穴浓度(p)与Mn浓度(x)的关系。结果表明，随着x的增加，T_c和p单调增加，可达0.05左右。对于x=0.053.2的样品，到目前为止获得的最高T_c为110 K。实现了所有基于半导体的铁磁/非磁量子结构，（Ga, Mn） As/(Al, Ga) As异质结构。即使在这种结构中，（Ga, Mn） As层的厚度小于10 nm，铁磁秩序仍然保持不变。通过对顺磁区磁电阻的分析，确定了磁自旋与空穴之间交换作用的大小（J_<pd>）。这个J_<pd>足够大，可以用well RKKY公式很好地解释观测到的T_c。这些结果有力地表明，利用场效应晶体管结构通过电场改变载流子浓度来控制（Ga, Mn） As的磁性是可能的。

The purpose of this research is to clarify the relationship between magnetism and semiconductor properties such as carrier concentration, and to explore the possibility of control of magnetism by the control of carrier concentration, using III-V based diluted magnetic semiconductor quantum structures. Here, we concentrated mainly on (Ga, Mn) As which we showed earlier that it can be grown by lowtemperature molecular-beam epitaxy and shows hole-induced ferromagnetic order at low temperaturcs.The summary of results is as follows ;1.From magnetotransport measuremens, the dependence of ferromagnetic transition temperature (T_c) and hole concentration (p) of (Ga, Mn) As on the Mn concentration (x) was determined. It is showm that both T_c and p monotonically increase with increase of x up to about 0.05. The highest T_c obtained so far is 110 K for a sample with x=0.053.2.All semiconductor-based ferromagnetic/non-magnetic quantum structures, (Ga, Mn) As/(Al, Ga) As heterostructures were realized. Even in such structures, where the thickness of (Ga, Mn) As layrs is below 10 nm, the ferromagnetic order is preserved.3.From the analysis of the magnetoresistance in the paramagnetic region, the magnitude of exchange interaction (J_<pd>) between magnetic spins and holes was determined. This J_<pd> is shown to be large enough to explain the observed T_c by the well RKKY formula remarkably well.These results strongly indicates that it is possible to control the magnetism of (Ga, Mn) As by changing the carrier concentration of the layrs by electric fields using field effect transistor structures.