【作者】 罗敏；

【导师】 唐政；

【作者基本信息】 华东师范大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 GMR效应的发现使人们对电子自旋的研究越来越关注,由此出现新的学科——半导体自旋电子学。跟传统的半导体器件相比,半导体自旋器件具有速度快、体积小、能耗小等特点,应用潜力巨大。稀磁半导体作为制备自旋半导体器件的重要材料,一直是材料科学的研究热点。GMR效应是在铁磁材料和非磁性材料交替组合成的多层膜结构中出现的一种磁阻效应；目前,人们主要是在合金材料中实现了这种GMR效应。而稀磁半导体同时具备了磁性和半导体性,因此,人们对一系列稀磁半导体的多层结构进行了详细的研究,但相关的理论和实验工作都表明,稀磁半导体的多层结构的层间交换耦合以铁磁耦合为主,很少有反铁磁耦合的报道。本文用第一性原理的理论方法研究了Mn掺杂GaAs基稀磁半导体多层结构的层间交换耦合以及Mn和Cu掺杂GaN基稀磁半导体多层结构的层间交换耦合。我们的主要结论是：(Ga,Mn)As的多层结构取决GaAs非磁性层的厚度和Be(载流子)掺杂的位置。对于纯的GaAs非磁性层,(Ga,Mn)As的层间交换耦合始终是铁磁耦合,这可以用有能隙系统的RKKY作用来解释,而通过Be掺杂,其层间交换耦合可以由铁磁耦合转成反铁磁耦合,跟实验结果一致。层间交换耦合转变的关键在于Mn-Be之间s-d杂化的强弱,较强的s-d杂化能够有效地传递两(Ga,Mn)As磁层间的反铁磁耦合作用。研究表明,载流子对层间交换耦合的调控起着关键的作用。此外,我们还研究了电场对(Ga,Mn)As多层结构的层间交换耦合的影响,计算结果显示,其层间交换耦合随着电场强度的变化呈现出周期性的变化。Mn和Cu掺杂的GaN多层结构的层间交换耦合,对于纯的GaN非磁性层的情况,基态都是铁磁耦合,同样可以用有能隙系统的RKKY作用来解释。而对于Mg掺杂的GaN非磁性层的情况,Mn和Cu掺杂体系的结果差异很大：对(Ga,Mn)N结构,随着Mg掺杂的GaN非磁性层厚度的增加,其层间交换耦合会逐渐由铁磁耦合转变成反铁磁耦合；而(Ga,Cu)N结构,当2个Mg同时掺杂在上下界面层时,其层间交换耦合直接表现为反铁磁耦合。两者差异的主要原因是,在费米能级附近, Cu-Mg间的sp-d杂化强度比Mn-Mg间的sp-d杂化强度强很多。由于Mn和Cu分别是磁性元素和非磁性元素,所以这两种体系的对比结果很有意义,这些结果表明：Cu元素对于GaN基的稀磁半导体而言可能是更好的掺杂元素。更多还原

【Abstract】 The GMR effect has initiated spintronics and with the discovery of diluted magnetic semiconductors a new field of semiconductor spintronics has emerged. Compared to the traditional semiconductor devices, the spin devices have powerful potential values and have more advantages, such as quick working speed, small size, and lower energy consumption. Diluted magnetic semiconductors are important materials for the applications of spintronics devices and recently are becoming a hotspot of materials science.The GMR effect is a magnetoresistance effect observed in the multilayers which are stagger stacked by ferromagnetic and nonmagnetic metallic materials. The Diluted magnetic semiconductors (DMS) have both magnetic property and semiconductor property. Therefore, a lot of detailed works have been done about the interlayer exchange coupling (IEC) in a series diluted magnetic semiconductors multilayers. However, usually, only ferromagnetic IEC was observed in DMS multilayers and only very recently, the antiferromagnetic IEC in Be-doped DMS multilayer systems was reported. In this thesis, we studied the IEC of both Mn doped GaAs-based DMS magnetic multilayers, and Mn and Cu doped GaN-based DMS magnetic multilayers by first-principles calculations.It is found that, the IEC of the multilayers of (Ga,Mn)As is decided by both the thickness of pure GaAs nonmagnetic layers and Be substitutions in GaAs nonmagnetic spacer. For the pure GaAs nonmagnetic layers, the ferromagnetic IEC is always achieved which can be explained by the RKKY interaction with a gap in materials, the calculating result is consistent to the experimental results. The key of the tunable IEC is the s-d interaction, the strong s-d interaction can effectively mediate the spin interaction between the ferromagnetic (Ga, Mn)As layers. From the calculations, we conclude that the carrier plays an important role in the IEC. Moreover, we also study the relationship between the electric field and the IEC and we observe that the IEC shows a periodical variety as the electric field changing.For the Mn and Cu doped GaN-based multilayers systems, with the pure GaN nonmagnetic layers, the ground states are ferromagnetic for two systems which can also be explained by the RKKY interaction with a gap in materials. However, the results are quite different when Mg-doped GaN nonmagnetic spacers. For the (Ga,Mn)N system, the IEC can be transferred from ferromagnetic to antiferromagnetic gradually, with the GaN spacer’s thickness increasing. But for the (Ga,Cu)N system, the antiferromagnetic IEC is immediately achieved when two Mg atoms are doped into the interfaces between the (Ga, Cu)N layers and the spacers. The main difference is that the Cu-Mg hybridization has a stronger sp-d hybridization (compared with the Mn-Mg hybridization) around the Fermi energy level. These results indicate that Cu is a better dopant for the device application of the GaN-based DMS magnetic multilayers.更多还原