Spin Control in Semiconductor Nanostructures

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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