氧化物稀磁半导体铁磁性的缺陷调节机制研究

Conventional semiconductors only take advantage of charge freedom while diluted magnetic semiconductors simutaneously exploit both charge and spin freedoms. Spintronics devices made of diluted magnetic semiconductors are promising to integrate data processing and storage, and have much prospective applications. Previously, researchers designed to prepare diluted magnetic semiconductors by doping magetic elements into semiconductors. However, studies show that magnetic elements introduced into semiconductors do not lead to ferromagnetism directly and ferromagnetism often relates to the presence of intrinsic vacancies in semiconductors. Therefore, by adjusting and controlling the defects and vacancies, room temperature ferromagnetism can be obtained in the doped semiconductors. Up to now, the mechnism of vacancy-mediated ferromagnetism still remains unclear. We plan to investigate the magnetic properties of the oxide semiconductors, i.e. SnO2, TiO2 and ZnO, doped by nonmagnetic elements, via first-principles calculations. We will study the magnetic properties arising from the doped nonmagnetic elements and intrinsic vacancies in order to find the potential systems with room-temperature ferromagnetism. We will also study how the quantum effect of size and impurity charge states affect the splitting of spin-polarized bands and the magnetic couplings respectively. The orgin of ferromagnetism will be studied in this project. Furthermore, the formation energies of impurities and vacancies as functions of atom chemical potentials wil be studied to predict the most beneficial ambient in experimental preparations.

传统半导体技术只利用了电荷自由度，而稀磁半导体则同时利用了电荷和自旋自由度。由稀磁半导体制备的新型自旋电子学器件有望将数据处理与存储融为一体，具有广阔的应用前景。此前人们向半导体中掺入磁性元素以期获得铁磁性半导体，但是研究表明磁性元素的引入并不能直接导致半导体的铁磁性，铁磁性的出现与半导体中的本征缺陷具有密切关系。通过同时引入过渡元素杂质和本征缺陷可以获得室温以上的铁磁性。目前关于铁磁性的缺陷调节机制的理论研究尚不明确。我们拟采用第一性原理计算方法对SnO2、TiO2和ZnO等氧化物半导体的薄膜和纳米线进行掺杂研究。计算半导体中同时引入非磁性杂质和本征缺陷对磁性影响，寻找具有室温铁磁性的半导体掺杂体系；研究量子限制效应对自旋能带的劈裂以及杂质电荷态对磁性的影响；解释低浓度掺杂下材料的铁磁性起源；研究杂质与缺陷态的形成能与原子化学势的关系，为实验上制备高稳定性的稀磁半导体作出指导

自旋电子学的兴起为计算机科学提供了新的技术支持。磁性半导体是自旋电子学器件的核心材料，该材料同时利用了电子的自旋与电荷自由度，有望将数据处理和存储集为一体。磁性半导体的研究重点是如何让半导体获得室温以上的铁磁性且半导体性质不被破坏。目前磁性半导体主要将过渡金属掺入宽禁带半导体如SnO2, ZnO和TiO2等材料中获得。尽管具有室温铁磁性的半导体在很多实验中被合成，但是其铁磁性机制却没有仍然没有明白。目前氧化物半导体的铁磁性机制研究大多集中在氧缺陷方面，而阳离子缺陷导致的铁磁性却被很多研究者所忽略，因此我们的研究重点在于探讨过渡金属掺杂的氧化物半导体中的铁磁性起源，研究铁磁性究竟是起源于阴离子缺陷还是阳离子缺陷。我们重点研究了Cu、Mn掺杂的SnO2和Cd掺杂的TiO2的铁磁性，在研究中我们全面比较了阳离子和阴离子缺陷所带来的调节机制，给出了相应的阳离子缺陷调节机制图景，解释了相应铁磁性的起源，理论计算结果与实验符合较好。成果发表在<Journal of Applied Physics>上两篇，发表在<Physica B>上面一篇。这些成果对过渡金属掺杂的半导体的磁性起源给出了解释，讨论相应的缺陷调节机制，对磁性半导体的制备提供了很好的建议。