Mn掺杂GaN稀磁半导体的电磁特性研究

采用基于密度泛函理论的第一性原理平面波超软赝势法计算了不同浓度Mn掺杂GaN(Ga1-xMnxN,x=0.0625和0.1250)的晶格常数、能带结构和态密度,分析比较了掺杂前后GaN的电子结构和磁性.结果表明:Mn掺入后体系仍为直接带隙半导体,带隙宽度随Mn含量的增加逐步增大.Mn掺杂GaN均使得N2p与Mn3d轨道杂化,产生自旋极化杂质带,自旋向上的能带占据费米面,掺杂后的Ga1-xMnxN表现为半金属铁磁性,适合自旋注入;随着Mn掺杂浓度的增加,体系的半金属性有所增强.     

Mn掺杂GaN电子结构和光学性质研究

采用基于密度泛函理论的第一性原理平面波赝势法计算不同Mn浓度掺杂GaN晶体的电子结构和光学性质.计算结果表明Mn掺杂GaN使得Mn 3d与N 2p轨道杂化,产生自旋极化杂质带,材料表现为半金属性,非常适于自旋注入,说明该种材料是实现自旋电子器件的理想材料,折射率在带隙处出现峰值,紫外区光吸收系数随Mn浓度的增加而增大. 关键词： Mn掺杂GaN 第一性原理 电子结构 光学性质     

Mn掺杂对半金属铁磁体Fe_2Si电磁特性的影响

此文用基于密度泛函理论第一性原理的贋势平面波方法,计算了Fe_2Si及Mn掺杂Fe_2Si体系的能带结构、电子态密度和磁学特性,分析了不同位置Mn掺杂对Fe_2Si电磁特性的影响,获得了纯的和不同位置Mn掺杂的Fe_2Si体系是铁磁体,自旋向上的能带结构穿过费米面表现金属特性,纯Fe_2Si的半金属隙为0.164e V;Mn掺杂在Fe1位时,自旋向下部分转变为A-M间的间接带隙半导体,体系呈现半金属特性,此时磁矩为2.00μB,是真正的半金属性铁磁体;掺杂在Fe2位时,自旋向下部分的带隙值接近于0,体系呈现金属特性;掺杂在Fe3位时,自旋向下部分转变为L-L间的直接带隙半导体,体系呈现半金属特性等有益结果 .自旋电荷密度分布图表明Mn原子的3d电子比较局域,和周围原子成键时3d电子更倾向于形成共价键.体系的半金属性和磁性主要来源于Fe-3d电子与Mn-3d电子之间的d-d交换,Si-3p电子与Fe、Mn-3d电子之间的p-d杂化.这些结果为半金属铁磁体Fe_2Si的电磁调控提供了有效的理论指导.     

空位缺陷及Mg替位对纤锌矿(Ga,Mn)N电子结构和磁光性能的影响

采用自旋密度泛函理论框架下的广义梯度近似(GGA+U)平面波超软赝势方法,构建了未掺杂纤锌矿GaN超胞、三种不同有序占位Mn双掺GaN,(Mn,Mg)共掺杂GaN以及存在空位缺陷的Mn掺杂GaN超胞模型,分别对所有模型的能带结构、电子态密度、能量以及光学性质进行了计算.计算结果表明:与纯的GaN相比,Mn掺杂GaN体系的体积略有增大,掺杂体系居里温度能够达到室温以上;随着双掺杂Mn-Mn间距的增大,体系总能量和形成能升高、稳定性下降、掺杂越难;(Mn,Mg)共掺杂并不能有效增大掺杂体系磁矩,也不能达到提高掺杂体系居里温度的作用;Ga空位缺陷和N空位缺陷的存在不利于Mn掺杂GaN形成稳定的铁磁有序.此外,Mn离子的掺入在费米能级附近引入自旋极化杂质带,正是由于费米能级附近自旋极化杂质带中不同电子态间的跃迁,介电函数虚部在0.6868eV附近、光吸收谱在1.25eV附近分别出现了一个较强的新峰.     

Cr掺杂浓度对AlN半金属性影响的第一性原理研究

本文基于密度泛函理论的第一性原理方法, 在广义梯度近似(GGA)下计算了掺杂过渡金属Cr原子后AlN晶体自旋极化的能带结构、分态密度等性质. 结果表明, 半金属能隙随着掺杂浓度的增大而减小. 文中以掺杂浓度为12.5%的Cr-AlN(2×2×1)为例, 分析了其自旋极化的能带结构、分态密度和磁矩等性质, 发现Cr-3d电子对自旋向下子带导带底的能量位置起决定作用. 随着掺杂浓度的增大, Cr原子间相互作用增强, Cr-3d能带向两边展宽, 导致自旋向下子带导带底的能量位置下降, 从而半金属能隙变窄.     

Cr掺杂浓度对AlN半金属性影响的第一性原理研究

本文基于密度泛函理论的第一性原理方法, 在广义梯度近似(GGA)下计算了掺杂过渡金属Cr原子后AlN晶体自旋极化的能带结构、分态密度等性质. 结果表明, 半金属能隙随着掺杂浓度的增大而减小. 文中以掺杂浓度为12.5%的Cr-AlN(2×2×1)为例, 分析了其自旋极化的能带结构、分态密度和磁矩等性质, 发现Cr-3d电子对自旋向下子带导带底的能量位置起决定作用. 随着掺杂浓度的增大, Cr原子间相互作用增强, Cr-3d能带向两边展宽, 导致自旋向下子带导带底的能量位置下降, 从而半金属能隙变窄.     

p，n型掺杂剂与Mn共掺杂GaN的电磁性质

采用基于密度泛函理论的第一性原理平面波赝势法计算Mg,Zn,Si,O和Mn共掺GaN,分析比较共掺杂后的电子结构和磁学性质,并分别用平均场近似的海森伯模型和Zener理论估算共掺杂后体系的居里温度（T_C）.计算表明：共掺杂后体系均在能隙深处产生自旋极化杂质带,具有半金属性,能产生自旋注入.p型共掺杂（GaN：Mn-Mg＼Zn）后体系具有较GaN：Mn更稳定的FM态且能使T_C升高;而n型共掺杂（GaN：Mn-Si＼O）后体系FM态稳定性 关键词： Mg Zn Si O和Mn共掺GaN 第一性原理 T_C）')" href="#">居里温度（T_C）     

共轭低聚物中光生分子间电荷转移态的第一性原理研究（英文）

本文基于第一性原理中的Heyd-Scuseria-Ernzerh方法研究了单层In_(1-x)Ga_xN的电子结构和光学性质.计算得到单层In_(1-x)Ga_xN的能带结构和态密度(DOS),发现随着掺杂比例的变化,体系带隙的变化范围是1.8～3.8 eV,表明通过Ga的掺杂可以实现体系带隙值的调节.并且还研究了单层In_(1-x)Ga_xN的介电函数,折射率和吸收系数等光学性质,结果表明随着Ga掺杂浓度的增加,介电函数谱的主峰和吸收谱发生了显著的蓝移.此外,基于能带结构和态密度图谱,对单层In_(1-x)Ga_xN的光学性质进行分析,预测这种材料独特的光学性质在纳米电子学和光学器件中会有广泛的应用.     

锰掺杂二硅化铬电子结构和光学性质的第一性原理计算

采用基于第一性原理的密度泛函理论(DFT)赝势平面波方法计算了锰掺杂二硅化铬(CrSi2)体系的能带结构、态密度和光学性件质.计算结果表明末掺杂CrSi2属于间接带隙半导体间接带隙宽度△ER=0.35 eV;Mn掺杂后费米能级进入导带,带隙变窄,且间接带隙宽度△Eg=0.24 eV,CrSi2转变为n型半导体.光学参数发生改变,静态介电常数由掺杂前的ε1(O)=32变为掺杂后的ε1(O)=58;进一步分析了掺杂对CrSi2的能带结构、态密度和光学性质的影响,为CrSi2材料掺杂改件的研究提供r理论依据.     

第一性原理研究In,N共掺杂SnO2材料的光电性质

采用全电势线性缀加平面波(FP-LAPW)的方法,基于密度泛函理论第一性原理结合广义梯度近似(GGA),运用Wien2k软件计算了In, N两种元素共掺杂SnO₂材料的电子态密度和光学性质. 研究表明,共掺杂结构在自旋向下和向上两方向上都出现细的局域能级,两者态密度分布不对称;带隙内自旋向下方向上产生局域能级,共掺化合物表现出半金属性;能带结构显示两种共掺杂化合物仍为直接禁带半导体,价带顶随着N浓度的增加发生向低能方向移动,带隙明显增宽;共掺下的介电函数虚部主介电峰只在8.58 eV 关键词： 电子结构 态密度 能带结构 光学性质     

Role of defect sites and Ga polarization in the magnetism of Mn-doped GaN

We report a study of the Mn local structure, magnetism, and Ga moments in molecular beam epitaxy grown Mn-doped GaN films. Using x-ray absorption spectroscopy and magnetic circular dichroism, we find two distinct Mn sites and a Ga moment antiparallel to Mn. First-principles calculations reproduce this phenomenology and indicate that Mn preferentially populates Ga sites neighboring N split interstitial defects. These results show that defects may strongly affect the Mn ordering and magnetism, and that the GaN valence band is polarized, providing a long-range ferromagnetic ordering mechanism for Ga1-xMnxN.     

Antiferromagnetic coupling driven by bond length contraction near the Ga1-xMnxN film surface

Using first principles calculations based on gradient corrected density functional theory we show that Mn atoms, which couple ferromagnetically in bulk Ga1-xMnxN, couple antiferromagnetically on its surface. This change in magnetic behavior is brought about by a contraction of the Mn-Mn and Mn-N bond lengths, which is significantly greater on the surface than in the bulk. The present study provides new insight to the numerous conflicting experimental observations in Mn doped GaN systems.     

Local electronic structure around Mn and Ga in Mn-doped GaN films showing room temperature ferromagnetism

Local electronic structures around Ga and Mn in Mn-doped GaN film with T_c of 940 K are investigated by K X-ray absorption near edge structure (XANES) analysis. It was found that the shape of the Ga XANES spectrum is remarkably similar to that of the un-doped GaN film indicating that the local electronic structure around Ga is not disturbed with Mn doping. As for the Mn XANES spectra, obvious pre-edge peaks were observed: the fine structures in the pre-edges correspond with calculated Mn 3d partial density of states which predict impurity band formation with the Fermi energy stays in the spin-up band. These findings imply that Mn 3d levels stay within the gap with the Fermi energy stays in the spin-up band.     

应变对两层半氢化氮化镓薄膜电磁学性质的调控机理研究

采用基于密度泛函理论的第一性原理模拟计算,研究了在应变作用下两层半氢化氮化镓纳米薄膜的电学和磁学性质.没有表面修饰的两层氮化镓纳米薄膜的原子结构为类石墨结构,并具有间接能隙.然而,当两层氮化镓纳米薄膜的一侧表面镓原子被氢化时,该纳米薄膜却依然保持纤锌矿结构,并且展示出铁磁性半导体特性.在应变作用下,两层半氢化氮化镓纳米薄膜的能隙可进行有效调控,并且它将会由半导体性质可转变为半金属性质或金属性质.这主要是由于应变对表面氮原子的键间交互影响和p-p轨道直接交互影响之间协调作用的结果.该研究成果为实现低维半导体纳米材料的多样化提供了有效的调控手段,为其应用于新型电子纳米器件和自旋电子器件提供重要的理论指导.     

金属有机化学气相淀积技术制备GaMnN薄膜材料光学性质研究

研究由MOCVD 技术制备的 GaMnN 外延薄膜光吸收谱.实验发现Mn掺杂后较未掺杂GaN吸收系数在近紫外区增加,在吸收谱低能区144 eV附近观察到吸收峰,吸收系数随Mn浓度的增加而增大.实验结果与基于密度泛函理论的第一性原理计算结果一致,结合理论计算分析认为144 eV附近的吸收峰源于Mn³⁺离子e态与t₂态间的带内跃迁⁵T₂→⁵E. 关键词： GaMnN MOCVD 密度泛函理论 光学性质     

Electronic Structures of Wurtzite GaN with Ga and N Vacancies

The electronic band structures of wurtzite GaN with Ga and N vacancy defects are investigated by means of the first-principles total energy calculations in the neutral charge state. Our results show that the band structures can be significantly modified by the Ga and N vacancies in the GaN samples. Generally, the width of the valence band is reduced and the band gap is enlarged. The defect-induced bands can be introduced in the band gap of GMV due to the Ga and N vacancies. Moreover, the GaN with high density of N vacancies becomes an indirect gap semiconductor. Three defect bands due to Ga vacancy defects are created within the band gap and near the top of the valence band. In contrast, the N vacancies introduce four defect bands within the band gap. One is in the vicinity of the top of the valence band, and the others are near the bottom of the conduction band. The physical origin of the defect bands and modification of the band structures due to the Ga and N vacancies are analysed in depth.     

Magnetic properties of (Ga,Mn)N ternaries and structural,electronic, and magnetic properties of cation-mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries

ABINIT simulation package with built in local density, generalized gradient, and spin local density approximations was used to investigate the structural, electronic, and magnetic properties of cation mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries with equal and fixed compositions of Ga, In, and Mn atoms. In particular, total energy minimization approach was used to compute the equilibrium structural parameters of zinc-blende (GaAs, InAs, and MnAs), wurtzite (GaN, InN, and MnN) binary parent compounds, as well as, the corresponding equilibrium parameters of (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternary systems. The band structures of zinc-blende GaAs, InAs, and MnAs binary parent compounds were computed and analyzed. Spin polarized band structures of the cation mixed (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries with equal compositions of Ga, In, and Mn cations were computed and analyzed using spin local density approximation based calculations. Moreover, the magnetic properties of (Ga,Mn)(As,N) and (In,Mn)(As,N) quaternaries with equal concentration of Ga, In, and Mn cations were investigated. Our results suggest that the two quaternary systems are nonmagnetic. An interpretation of our results is presented. In addition, the magnetic properties of (Ga,Mn)N nanocrystal ternaries constructed from doping GaN with one or two Mn atoms were investigated using Vienna Ab-initio Simulation Package (VASP) and compared with those of (Ga,Mn)(As,N) quaternaries.     

Concerted diffusion, clustering, and magnetic properties of Mn dopants on a 2 x 2-T4 GaN(0001) substrate

Based on first-principles calculations within density functional theory, we propose a kinetic pathway for Mn incorporation on reconstructed 2 x 2-T4 GaN(0001), characterized by concerted substitution of a Ga atom by a Mn adatom via a precursor surface site T4. The Mn dopants at low densities are randomly distributed, resulting in intrinsic diluted magnetic semiconductors (DMS). At high Mn densities, planar ferromagnetic clusters oriented in the (0001) plane can be readily formed at relatively low growth temperatures, but ferrimagnetic zigzag columns along the growth orientation will be formed at high temperatures. Furthermore, intrinsic DMS are more likely to be formed via codeposition of Mn+Ga+N at high growth rates. These findings help to explain the observed variations in both the magnetic ordering temperature TC and the magnetic nature of Ga1-xMnxN.     

热退火对Mn离子注入非故意掺杂GaN微结构、光学及磁学特性的影响

通过Mn离子注入非故意掺杂GaN外延层制备了GaN:Mn薄膜,并研究了退火温度对GaN:Mn薄膜的微结构、光学及磁学特性的影响.对不同退火温度处理后的GaN:Mn薄膜的拉曼谱测试显示,出现了由与离子注入相关的缺陷的局域振动(LV)和(Ga,Mn)N中Mn离子的LV引起的新的声子模.在GaN:Mn薄膜的光致发光谱中观察到位于2.16,2.53和2.92 eV处的三个新发光峰(带),其中位于2.16 eV处的新发光带不能排除来自Mn相关辐射复合的贡献.对GaN:Mn薄膜的霍尔测试显示,退火处理后样品表现出n型体材料特征.对GaN:Mn薄膜的振动样品磁强计测试显示,GaN:Mn薄膜具有室温铁磁性,其强弱受Mn相关杂质带中参与调节磁相互作用的空穴浓度的影响.