N空位对Cu掺杂AlN电磁性质的影响的第一性原理研究

利用基于密度泛函理论的平面波超软赝势法研究了N空位对Cu掺杂AlN的电子结构和磁学性质的影响.结果表明,与Cu最近邻的N原子更易失去形成N空位.N空位的引入减小了Cu掺杂AlN体系的半金属能隙;减弱了Cu及其近邻N原子的自旋极化的强度以及Cu3d与N2p轨道间的杂化,因而减小了体系的半金属铁磁性.因此,制备Cu掺杂AlN稀磁半导体时应尽可能地避免N空位的产生.     

Cu、Ag和Au掺杂AlN的电磁性质的第一性原理研究

采用基于密度泛函理论（DFT）的平面波超软赝势法,研究了Cu、Ag、Au掺杂AlN的晶格常数、磁矩、能带结构和态密度。电子结构表明,Cu、Ag、Au的掺杂使在带隙中引入了由杂质原子的d态与近邻N原子的2p态杂化而成的杂质带,都为p型掺杂,增强了体系的导电性。Cu掺杂AlN具有半金属铁磁性,半金属能隙为0.442eV,理论上可实现100%的自旋载流子注入;Ag掺杂AlN具有很弱的半金属铁磁性;而Au掺杂AlN不具有半金属铁磁性。因此,与Ag、Au相比,Cu更适合用来制作AlN基稀磁半导体。     

Cu掺杂的AlN铁磁性和光学性质的第一性原理研究

采用基于密度泛函理论（DFT）的总体能量平面波超软赝势方法,结合广义梯度近似（GGA）,对Cu掺杂AlN 32原子超原胞体系进行了几何结构优化,计算了Cu掺杂AlN的晶格常数,能带结构,电子态密度和光学性质.结果表明,Cu掺杂AlN会产生自旋极化状态,能带结构显示半金属性质,掺杂后带隙变窄,长波吸收加强,能量损失明显减小.同传统的稀磁半导体（DMS）相比,Cu掺杂AlN不会有铁磁性沉淀物的问题,因为Cu本身不具有磁性.因而,Cu掺杂的AlN也许是一种非常有前途的稀磁半导体. 关键词： AlN 第一性原理 铁磁性 光学性质     

Ti,Cu和Zn掺杂AlN纳米片电磁性质的第一性原理研究

采用基于密度泛函理论(DFT)的全势线性缀加平面波法(FP-LAPW)研究了过渡金属Ti,Cu,Zn掺杂Al N纳米片的电子结构、磁性和稳定性.结果表明,Ti,Cu,Zn单掺杂均表现出半金属铁磁性,磁性主要是由于杂质原子的3d态与近邻N原子的2p态的轨道杂化.形成能的计算结果表明Ti掺杂Al N体系相对Cu和Zn掺杂结构更稳定.因此,相比于Cu和Zn,Ti掺杂Al N纳米片更适合用来制作稀磁半导体.     

不同浓度Cu掺杂AlN的电子结构和光学性质研究

采用基于密度泛函理论的平面波超软赝势和广义梯度近似的第一性原理计算方法,对理想纤锌矿AlN及不同浓度的Cu掺AlN的超晶胞结构进行了几何优化,计算并分析了它们的电子结构、磁电性质和光学性质.结果表明,掺杂后Cu3d态电子与其近邻的N2p态电子发生杂化,在带隙中引入杂质带,6.25%和12.5%的Cu掺杂体系表现出半金属铁磁性,体系总磁矩分别为2.56μв和2.42μв,25%的Cu掺杂体系表现出金属性.随着Cu浓度的增加,体系铁磁性反而减弱.Cu掺杂后体系介电函数虚部和复折射率函数在低能区发生明显变化,增强了体系对低频电磁波的吸收.当Cu浓度增加时体系对高频电磁波的吸收也随之加强.     

Ga空位对GaN:Gd体系磁性影响的第一性原理研究

采用基于密度泛函理论的第一性原理结合投影缀加平面波的方法,研究了GaN中Ga被稀土元素Gd替代以及与邻近N或Ga空位组成的缺陷复合体的晶格常数、磁矩、形成能以及电子结构等性质.结果发现,Gd掺杂GaN后禁带宽度变窄,由直接带隙半导体转为间接带隙半导体;单个Gd原子掺杂给体系引入大约7μB的磁矩;在Gd与Ga或N空位形成的缺陷复合体系中,N空位对引入磁矩贡献很小,大约0.1μB,Ga空位能引入约2μB的磁矩.随着Ga空位的增多,体系总磁矩增加,但增加量与Ga空位的位置分布密切相关.当Ga空位分布较为稀疏时,Gd单原子磁矩受影响较小,但当Ga空位距离较近且倾向于形成团簇时,Gd单原子磁矩明显增加,而且这种情况下空位形成能也最小.     

非金属N和过渡金属(Mo, Ru, Rh, Pd)掺杂SnO2磁性的第一性原理研究

本文基于第一性原理方法,对非金属元素(N)与过渡金属元素(Mo, Ru, Rh, Pd)掺杂SnO₂的电子结构和磁学性质进行计算分析.结果表明：形成能与过渡金属原子半径密切相关,随着过渡金属原子半径的增加,形成能在降低,其中N-Mo掺杂体系形成能最低,故该体系最容易掺杂形成;能带结构分析表明,由于掺杂体系自旋向上/向下杂质能级的数量和分布均不对称,掺杂体系均有磁性产生;进一步探究态密度可知,体系产生磁性的原因是过渡金属原子和N原子之间产生p-d轨道杂化,最外层电子轨道上的空位及单电子相互耦合所导致.结果表明,由于掺杂原子的引入,SnO₂体系产生磁性,并且掺杂体系呈现亚铁磁性,其中N-Rh掺杂体系的磁性最好,其磁矩为1.88μB,有望成为良好的稀磁半导体材料.     

5d过渡金属原子掺杂氮化铝纳米管电子结构、磁性性质的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理计算方法, 研究了5d过渡金属原子(Lu、Hf、Ta、W、Re、Os、Ir、Pt、Au、Hg)取代AlN纳米管(AlNNTs)中的铝原子或氮原子时体系的几何结构、电子结构和磁性性质; 并且以理想AlN纳米管(AlNNTs)、Al缺陷体系(VAl)和N缺陷体系(VN)的结果作为对比. 研究发现: 5d 原子取代Al(Al5d)时体系的局域对称性接近于C3v, 但是取代N(N5d)时体系的局域对称性偏离C3v对称性较大; 当掺杂的5d元素相同时, Al5d的成键能比N5d的成键能大; 当掺杂体系相同时(Al5d或N5d), 其成键能基本上随着5d原子的原子序数的增大而降低; 掺杂体系中出现了明显的杂质能级, 给出了态密度等结果; 不同掺杂情况的磁矩不同, 总磁矩呈现出较强的规律性. 利用C3v对称性和分子轨道理论解释了过渡金属原子取代Al时杂质能级的产生和体系磁性的变化规律.     

5d过渡金属原子掺杂氮化铝纳米管电子结构、磁性性质的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理计算方法, 研究了5d过渡金属原子(Lu、Hf、Ta、W、Re、Os、Ir、Pt、Au、Hg)取代AlN纳米管(AlNNTs)中的铝原子或氮原子时体系的几何结构、电子结构和磁性性质; 并且以理想AlN纳米管(AlNNTs)、Al缺陷体系(VAl)和N缺陷体系(VN)的结果作为对比. 研究发现: 5d 原子取代Al(Al5d)时体系的局域对称性接近于C3v, 但是取代N(N5d)时体系的局域对称性偏离C3v对称性较大; 当掺杂的5d元素相同时, Al5d的成键能比N5d的成键能大; 当掺杂体系相同时(Al5d或N5d), 其成键能基本上随着5d原子的原子序数的增大而降低; 掺杂体系中出现了明显的杂质能级, 给出了态密度等结果; 不同掺杂情况的磁矩不同, 总磁矩呈现出较强的规律性. 利用C3v对称性和分子轨道理论解释了过渡金属原子取代Al时杂质能级的产生和体系磁性的变化规律.     

N掺杂对zigzag型石墨烯纳米带的能带结构和输运性质的影响

用第一性原理研究了N掺杂zigzag型石墨烯纳米带(z-GNRs)的能带结构、透射谱和电流电压特性,研究结果表明N掺杂将使得z-GNRs的能带结构中出现能隙,材料从金属转变为半导体;随着杂质浓度的增大,相同偏压下电流明显减小,同时体系费米面附近的透射率逐渐减小;z-GNRs的长度、宽度以及N原子的替代掺杂位置均会对输运性质产生影响,在宽度较小的情况下,掺杂浓度和掺杂位置两种因素共同影响体系的输运性质. 关键词： 石墨烯纳米带 N掺杂 能带结构 输运性质     

Copper-doped AlN polycrystalline powders: A class of room-temperature ferromagnetic materials

Cu-doped AlN polycrystalline samples were synthesized by a solid-state reaction. X-ray diffraction analysis revealed the hexagonal structure of the doped samples. Photoluminescence measurements reveal the substitution of Cu for Al in the AlN lattice. Clear hysteresis loops are observed in the M-H curves for the samples at 300 K, revealing room temperature ferromagnetism of the samples. Our experimental results verify that room temperature ferromagnetism is an intrinsic property of Cu-doped AlN.     

Effects of different dopants on switching behavior of HfO_2-based resistive random access memory

In this study the effects of doping atoms(Al, Cu, and N) with different electro-negativities and ionic radii on resistive switching of HfO2-based resistive random access memory(RRAM) are systematically investigated. The results show that forming voltages and set voltages of Al/Cu-doped devices are reduced. Among all devices, Cu-doped device shows the narrowest device-to-device distributions of set voltage and low resistance. The effects of different dopants on switching behavior are explained with deferent types of CFs formed in HfO2 depending on dopants: oxygen vacancy(Vo) filaments for Al-doped HfO2 devices, hybrid filaments composed of oxygen vacancies and Cu atoms for Cu-doped HfO2 devices,and nitrogen/oxygen vacancy filaments for N-doped HfO2 devices. The results suggest that a metal dopant with a larger electro-negativity than host metal atom offers the best comprehensive performance.     

First-principles study on electronic and magnetic properties of Cu-doped CdS

Based on the full-potential linearized augmented plane wave (FLAPW) method, the electronic structures and magnetic properties in Cu-doped CdS diluted magnetic semiconductors (DMSs) have been investigated. The results indicate that Cu-doped CdS systems show half-metallic character with a total magnetic moment of 1.0 μ_B per supercell. In the case of two Cu atoms substituting for Cd atoms, the long-range ferromagnetism is observed, which results from Cu(3d)-S(3p)-Cd-S(3p)-Cu(3d) coupling chain. The estimated Curie temperature of Cu-doped CdS is predicted to be 400 K, higher than room temperature. These results suggest that Cu-doped CdS may be a promising half-metallic ferromagnetic material for practical applications in electronics and spintronics.     

Half-metallic ferromagnetism in Cu-doped zinc-blende ZnO from first principles study

Electronic structures and magnetism of Cu-doped zinc-blende ZnO have been investigated by the first-principle method based on density functional theory (DFT). The results show that Cu can induce stable ferromagnetic ground state. The magnetic moment of supercell including single Cu atom is 1.0 μ_B. Electronic structure shows that Cu-doped zinc-blende ZnO is a p-type half-metallic ferromagnet. The half-metal property is mainly attribute to the crystal field splitting of Cu 3d orbital, and the ferromagnetism is dominated by the hole-mediated double exchange mechanism. Therefore, Cu-doped zinc-blende ZnO should be useful in semiconductor spintronics and other applications.     

First-principles study on the origin of ferromagnetism in n-type Cu-doped ZnO

Based on the density functional calculations with the GGA+U correction, we elucidate the origin of the experimentally reported ferromagnetism in n-type Cu-doped ZnO. Pure Cu-doped ZnO shows the unoccupied 3d states in the gap introduced by Cu, resulting in the insulating ground state and weak magnetic exchange interactions, in contrast to the half-metallic ground state and high ferromagnetic stability predicted by the calculations without U correction. However, the electron traps induced by Cu in n-type Cu-doped ZnO may lead to the partial occupancy of the Cu gap states, which stabilize the ferromagnetic ordering between two Cu atoms.     

Room-temperature ferromagnetism with high magnetic moment in Cu-doped AlN single crystal whiskers

Ferromagnetism is investigated in high-quality Cu-doped A1 N single crystal whiskers.The whiskers exhibit roomtemperature ferromagnetism with a magnetic moment close to the results from first-principles calculations.High crystallinity and low Cu concentrations are found to be indispensable for high magnetic moments.The difference between the experimental and theoretical moment values is explored in terms of the influence of nitrogen vacancies.The calculated results demonstrate that nitrogen vacancies can reduce the magnetic moments of Cu atom.     

Effect of Ar ion irradiation on the room temperature ferromagnetism of undoped and Cu-doped rutile TiO_2 single crystals

Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO_2 single crystals(SCs).To tune their magnetism,Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively.The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO_2.Meanwhile,a new CuO-like species present in the sample was found to be dissolved after the post-irradiation.Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions,while these ions are directly involved in boosting the absorption in the visible region.     

Ferromagnetic properties of Cu-doped ZnS: A density functional theory study

Using plane-wave pseudopotential (PWPP) method, the magnetism and spin-resolved electronic properties of Cu-doped ZnS system are studied. Our calculations indicate that ferromagnetic (FM) state is ground state in Cu-doped ZnS. The FM coupling strength in ZnS doping with Cu fluctuates with the variation of distance between two dopants and the fluctuation gets larger with increase in distance. Room temperature ferromagnetism can be observed in Cu-doped ZnS with high dopant concentration. Formation energy calculation implies that the clustering effect is not obvious in Cu-doped ZnS. Thus, Cu-doped ZnS can be a promising dilute magnetic semiconductor (DMS), which promises to be free of magnetic precipitates.