Study on high quality epitaxial growth of quantum well structures with II-VI diluted magnetic semiconductors

本论文的主要研究内容如下：1.制备由II-VI族化合物稀磁材料组成的量子线、量子点和量子威尔斯阱等纳米结构; 2.研究纳米结构中激子动力学和光自旋注入。电子束光刻法也被用于纳米结构的制造。制造的量子纳米结构进行了评估，通过X射线衍射和电子显微镜。利用飞秒激光光谱技术研究了强磁场下的光学性质。利用瞬态泵浦-探测光谱研究了这些稀磁纳米结构中激子的超快自旋动力学。在飞秒到纳秒的时间范围内研究了高密度电子空穴等离子体、激子和Mn离子的自旋动力学;在CdTe-CdMnTe双量子威尔斯中研究了自旋注入过程，量子阱激子的瞬态光致发光表现出快速的自旋注入和自旋弛豫过程;在ZnMnSe量子线结构中研究了磁光性质和激子动力学.在窄量子线中观察到明显的限制效应。在ZnTe-ZnMnTe自旋超晶格中阐明了自旋开关过程，其中在ZnTe和ZnMnTe层中激子的上自旋和下自旋态的分布在空间上被外磁场分离。这些现象有很高的自旋电子应用的可能性。

The objective of the research is following:1.Fabrication of nanostructures of quantum wires, quantum dots and quantum wells, which are composed of II-VI compound diluted magnetic semiconductors.2.Study of exciton dynamics and optical spin injection in the nanostructures.For the above objective, we fabricated the quantum nanostructures with CdTe, CdSe, ZnTe, ZnSe and magnetic materials of Mn by using molecular expitaxy and hot wall epitaxy. Electron beam lithography method was also used for nanostructure fabrications. Fabricated quantum nanostructures were evaluated by x-ray diffraction and electron microscopy. Optical properties were studied by femtosecond laser spectroscopy in high magnetic fields. Ultrafast spin dynamics of excitons was investigated in these diluted magnetic nanostructures by transient pump-probe spectroscopy. The spin dynamics in the high density electron-hole plasma, excitons, and Mn ions were clarified in the femotsecond to nanosecond time region.Spin injection processes were investigated in CdTe-CdMnTe double quantum wells, where the transient photoluminescence of quantum-well excitons showed fast spin injection and spin relaxation processes.Magnet-optical properties and exciton dynamics were studied in the quantum wire structures of ZnMnSe. Marked confinement effect was observed in the narrow quantum wires. Spin switching processes were clarified in ZnTe-ZnMnTe spin superlattices, where the distribution of up- and down-spin states of excitons was spatially separated in ZnTe and ZnMnTe layers by the external magnetic fields. These phenomena have high possibilities for spin electronic applications.