【作者】 高国营；

【导师】 姚凯伦；

【作者基本信息】 华中科技大学 ， 凝聚态物理， 2008， 博士

【摘要】 量子力学告诉我们,电子具有电荷和自旋双重属性,但过去的研究主要关注了电子的电荷属性,发展了传统的半导体学,人们忽视了电子的自旋属性。近二十年来,人们越来越关注电子的自旋属性,发展了一门新兴的学科—半导体自旋电子学。与传统的半导体器件相比,自旋电子器件有体积小、能耗低、速度快等优点,并且能够发展集半导体性和铁磁性为一体的多功能电子器件,具有很大的潜在应用价值。稀磁半导体和半金属铁磁体是制备自旋电子器件的重要材料,是凝聚态物理和材料物理研究的一个热点。计算机模拟与人工实验相比,有费用少和时间少等诸多优点。随着量子力学和固体理论等学科的不断完善,以及计算机性能的飞速发展,借助材料模拟软件模拟预言新材料越来越成熟。本文主要利用基于密度泛函理论的材料模拟软件Wien2k和CASTEP,对金红石TiO2基稀磁半导体、碱土金属氮化物和碳化物、以及半金属铁磁体的表面和界面,进行了磁性和电子结构的计算。金红石TiO2基稀磁半导体的研究表明,金红石TiO2掺杂V和Cr都具有铁磁性,并且其居里温度可能在室温或以上;考虑强关联因素时,掺杂体系从半金属性转变到了半导体性;氧空位对金红石TiO2掺杂Cr的电子结构和磁性有很大影响。对于碱土金属氮化物,我们的计算发现食盐结构的氮化物MX (M=Ca, Sr, Ba; X=N, P, As)中只有CaN、SrN和BaN具有半金属铁磁性,而闪锌矿结构的MX都具有半金属铁磁性;对于碱土金属碳化物,我们预言到食盐结构的SrC和BaC是半金属铁磁体,或至少能分别以PbS和PbSe为衬底外延生长SrC和BaC半金属铁磁薄膜;我们也预言了外延生长闪锌矿结构的CaC、SrC和BaC半金属薄膜的可能性;另外,居里温度的计算表明,食盐结构的SrC和BaC以及闪锌矿结构的CaC、SrC和BaC的居里温度都远远超过了室温。这使这些半金属体系在自旋电子器件中更加实用。闪锌矿结构CaC的(110)、(001)和(111)表面的计算表明,只有(110)面和以C为端面的(111)面维持了半金属铁磁性,这为外延生长CaC半金属薄膜有一定的指导作用;对于CrTe/ZnTe(001)界面,我们发现以Cr和Te为顶面的界面都保持了CrTe块材时的半金属性,但顶面却失去了半金属性。更多还原

【Abstract】 From the quantum mechanics, we know that the electron has charge and spin properties. Our previous studies mainly focused on the electronic properties of charge, and we developed the traditional semiconductor physics, but we ignored the electronic properties of spin. In the past twenty years, electronic spin has attracted more and more research interest, and a new field of semiconductor spintronics was formed. Compared to the traditional semiconductor devices, the spintronics devices have the advantages of smaller size, lower energy consumption, and quick working speed, and it can also produce new devices combining the electronic spin and charge, the potential application is very great. Diluted magnetic semiconductors and half-metallic ferromagnets are important materials used in spintronics devices, and it is a hot studying field in condensed matter physics and materials physics.Computational simulations have the advantage of lower cost and few time compared to artificial experiments. With the continuous improvement of quantum mechanics and solid state theory, and the rapid development of the capability of computers, predicting new functional materials with materials design codes becomes more and more powerful. In this thesis, using the materials design codes of Wien2k and CASTEP, we performed the studies of magnetism and electronic structure on the diluted magnetic semiconductors based on rutile Tio2, the alkaline-earth nitrides and carbides, and the surfaces and interfaces of half-metallic ferromagnets.The studies on diluted magnetic semiconductors based on rutile TiO2 indicate that both V- and Cr-doped rutile TiO2 behavior ferromagnetism, and the Curie temperatures are room-temperature or above it; There is a transition from a half-metal to a semiconductor when taking account of the Coulomb correlation interaction of 3d of Ti, V and Cr for these doping systems; in addition, the oxygen vacancy has large effect on the electronic structure and magnetism of Cr-doped rutile TiO2.For alkaline-earth nitrides, our calculations show that only CaN, SrN and BaN are half-metallic in all the rock-salt MX (M= Ca, Sr, Ba; X= N, P, As), but all the zinc-blende MX behavior half-metallic characteristic. For alkaline-earth carbides, we predict that rock-salt SrC and BaC are half-metallic ferromagnets, or at least the corresponding half-metallic ferromagnetic films can be grown on the semiconductor substrates of PbS and PbSe, respectively. We also predict the possibility of the epitaxial growth of zinc-blende CaC, SrC and BaC half-metallic films on appropriate semiconductor substrates; In addition, above room-temperature Curie temperatures are find for these alkaline-earth carbides, which makes them more promising candidates for the practical applications of spintronics devices.The calculations of the surfaces of zinc-blende CaC (110), (001) and (111) indicate that only the (110) surface and the C-terminate (111) surface maintain the half-metallic ferromagnetism as shown in bulk CaC, which is helpful for the epitaxial growth of zinc-blende CaC half-metallic ferromagnetic films; For the CrTe/ZnTe(001) interface, we find that both the Cr-terminate and Te-terminate CrTe/ZnTe(001) interfaces preserve the half-metallicity as shown in bulk zinc-blende CrTe, but the topmost surfaces lost the half-metallicity.更多还原