Spin Control in Semiconductor Nanostructures

本课题的目的是在理论研究和实验研究的基础上，发展磁性半导体纳米结构中材料设计和自旋控制方法，以控制电子自旋。材料设计组（理论组）基于理论和从头算电子结构计算，开发了一种控制磁性半导体纳米结构中量子尺寸效应、p-d杂化和载流子密度的自旋控制方法。材料设计小组（实验和晶体生长小组）通过改变量子尺寸、超结构和掺杂来控制自旋相互作用的方法。主要研究结果如下：为制备低电阻率p型ZnO，提出了一种新的基于从头计算的共掺杂Ga（或In， Al）给体和N受体共掺杂的价控方法。在成功控制ZnO价态的基础上，提出了一种制备高磁性mn掺杂p型ZnO的材料设计。结果表明，在不存在移动磁头的情况下，由于反铁磁超交换作用，反铁磁态比铁磁态更稳定。结果表明，与移动空穴共掺杂后，由于铁磁双交换作用，铁磁态比反铁磁态更稳定。通过从头计算，预测了V-、Cr-、Fe-、Co-和ni掺杂ZnO中磁性态的化学变化趋势。对于磁化强度的热力学涨落很重要的稀磁半导体，提出了一种新的束缚极化子的计算方法，并阐明了涨落的影响。我们成功地培育了新的人工材料，由铁磁金属（MnAs）和半导体（GaAs和Si）组成的不同异质结构，具有原子控制层厚度和热力学稳定性，III-V基磁性半导体（Ga, Mn）As及其量子异质结构，颗粒状铁磁金属（MnAs）嵌入GaAs和相关的磁光子晶体，我们还澄清了输运，光学，这些杂化材料的磁性能可用于各种自旋控制器件。在MnAs: GaAs/InGaAs超晶格中已经观察到自旋阀型磁电阻（MR），其中纳米级MnAs簇嵌入在GaAs层中。在GaAs衬底上生长了一种由纳米级MnSb点组成的颗粒膜，具有磁场敏感的电流电压特性。得到MR比>10000%。发现gemte薄膜具有相变特性，结晶后出现铁磁态，使我们能够通过激光结晶形成铁磁纳米结构。少

The purpose of the project is to develop the materials design and spin control method in magnetic-semiconductor nanostructures in order to control electron spin, based on theoretical studies and experimental studies. Material design group (theory group) contributes to develop a spin control method with controlling the quantum size effect, p-d hybridization, and carrier densities in the magnetic-semiconductor nanostructures based upon the theory and ab initio electronic structure calculation. Material design group (experimental and crystal growth group) contributes to find a method for controlling spin interaction with changing the quantum size, super structure, and doping. The major results are as follows.1. A new valence control method of codoping with doping Ga (or In, Al) donor and N acceptor was developed in order to fabricate a low resistivity p-type ZnO based on ab initio calculation.2. Based upon the success in the valence control of ZnO, a material design was proposed to fabric … More ate ferromagnetic Mn-doped p-type ZnO.It is shown that the anti-ferromagnetic states is more stable than the ferromagnetic ones due to the anti-ferromagnetic super-exchange interaction, if there is no mobile hoes. Upon codoping with the mobile holes, it is shown that ferromagnetic state becomes more stable than anti-ferromagnetic state due to the ferromagnetic double-exchange interaction. Chemical trends of the magnetic state in V-, Cr-, Fe-, Co-, and Ni-doped ZnO were predicted based on the ab initio calculation.3. As for diluted magnetic semiconductors, in which thermodynamic fluctuation of magnetization is important, a new calculation method for the bound magnetic polaron is developed and the effect of the fluctuation is claified.4. We have successfully grown new artificial materials, dissimilar heterostructures consisting of ferromagnetic metal (MnAs) and semiconductor (GaAs and Si), with atomically controlled layer thickness and thermodynamic stability, III-V based magnetic semiconductor (Ga, Mn)As and its quantum heterostructures, granular ferromagnetic metal (MnAs) embedded in GaAs and related magneto-photonic crystals and also we have clarified the transport, optical, and magnetic properties of these hybrid materials which can be used for a variety of spin-controlled devices. Spin-valve type magnetoresistance (MR) has been observed in MnAs : GaAs/InGaAs superlattices, where nanoscale MnAs clusters are embedded in the GaAs layer. A granular film consisting of nanoscale MnSb dots grown on GaAs substrate was found to exhibit magnetic-field sensitive current voltage characteristics. MR ratio>10000% is obtained.It was found that the GeMnTe film has the phase change properties, and the ferromagnetic state appears after crystallization, which enables us to form ferromagnetic nanostructures by crystallization with laser-beam. Less