第一性原理研究应变Si/(111Si1-xGex能带结构

基于密度泛函理论框架的第一性原理平面波赝势方法对双轴应变Si/(111)Sil1-xGex(x=0.1-0.4)的能带结构进行了研究,结果表明:导带带边六度简并没有消除;应变部分消除了价带带边的简并度;导带带边能量极值k矢位置和极值附近可由电于有效质量描述的能带形状在应变条件下几乎小变;价带极大值附近可由空穴有效质量描述的能带形状随着x有规律地变化.此外,给出的禁带宽度与x的拟合关系同KP理论计算的结果一致,该量化数据对器件研究设计可提供有价值的参考.     

应变Si1-xGex能带结构研究

采用结合形变势理论的K.P微扰法建立了（001）,（101）和（111）面弛豫Si衬底上生长的应变Si_1-xGe_x（x≤0.5）的能带结构模型,获得了其导带带边能级、价带带边能级、导带劈裂能、价带劈裂能及禁带宽度随Ge组分（x）的函数变化关系,该量化数据对器件研究设计可提供有价值的参考． 关键词： 1-xGe_x')" href="#">应变Si_1-xGe_x K.P 法 能带结构     

关于Zn1-xBexO电子结构和光学性质的研究

采用基于密度泛函理论和平面波赝势技术的CASTEP程序对Zn_1-xBe_xO合金电子结构和光学性质进行了计算.当0≤x≤1,其带隙从0.963 eV变化到7.293 eV.分析了晶格畸变和能带间排斥效应对带隙的影响.当Be含量x=0.125,0.25,0.375,0.5,0.625,0.75时,a/b轴压应变控制着带隙变化;当x=0.875,1时,c轴压应变控制着带隙变化.能带间的p-d排斥影响价带顶变动,Γ_1v与Γ_1c之间排斥影响导带底变动.这些能带间的排斥效应被用来分析Zn_1-xBe_xO带隙变动.另外,也分析了Zn_1-xBe_xO介电函数虚部ε₂. 关键词： 带结构 光学性质 应变 排斥     

应变Si/(001)Si1-xGex空穴有效质量各向异性

基于应变Si/（001）Si_1-xGe_x材料价带E（k）-k关系模型,研究获得了其沿不同晶向的空穴有效质量.结果表明,与弛豫材料相比,应变Si/（001）Si_1-xGe_x材料价带带边（重空穴带）、亚带边（轻空穴带）空穴有效质量在某些k矢方向变化显著,各向异性更加明显.价带空穴有效质量与迁移率密切相关,该研究成 关键词： 应变Si 价带 空穴有效质量     

应变Si1－xGex/(111)Si空穴有效质量模型

利用应变Si_1-xGe_x/(111)Si材料价带E(k)-k关系,研究获得了沿不同晶向的空穴有效质量,并在此基础上,建立了空穴各向同性有效质量模型.结果表明,与弛豫材料相比,应变Si_1-xGe_x/(111)Si材料价带带边空穴有效质量各向异性更加显著,带边空穴各向同性有效质量随Ge组分明显减小.该研究成果可为Si基应变PM 关键词： 1-xGe_x')" href="#">应变Si_1-xGe_x 空穴有效质量 价带     

应变Si价带色散关系模型

基于K.P理论框架,通过引入应变哈密顿微扰项,详细推导并建立了应变Si的价带色散关系模型.所得模型适用于任意晶向弛豫Si_1－xGe_x(0≤x≤0.6)衬底上生长的应变Si,并且,通过该模型可以获取任意K矢方向的应变Si价带结构及空穴有效质量,对器件研究设计可提供有价值的参考. 关键词： 应变Si K.P理论 色散关系     

La0.1Bi0.9-xEuxFeO3化合物的结构与性能研究

利用固相反应烧结技术制备La_0.1Bi_0.9-xEu_xFeO₃系列化合物. 利用X射线粉末衍射进行物相鉴定和结构分析,确定了材料的相关系：x≤0.05,材料为R3c结构相;0.08≤x≤0.12,材料为赝R3c结构相;x≥0.15是Pbnm相,其中0.15≤x≤0.20区域Pbnm相存在畸变. 磁测量结果表明,材料具有弱铁磁性,对于x≤0.20材料,磁矩在x=0.12成分存在极值. 利用阻抗分析仪测量了室温介电常数随成分的变化关系.讨论了材料的结构与弱铁磁性和室温介电常数间的关系. 关键词： 0.1Bi_0.9-xEu_xFeO₃')" href="#">La_0.1Bi_0.9-xEu_xFeO₃ X射线衍射 磁性 介电常数     

Y掺杂SrTiO3晶体材料的电子结构计算

采用基于第一性原理的密度泛函理论平面波超软赝势法, 研究了Y掺杂SrTiO₃体系的空间结构和电子结构性质, 得到了优化后体系的结构参数, 掺杂形成能, 能带结构和电子态密度. 对比掺杂浓度为0125, 025, 033时,Sr_1-xY_xTiO₃和SrTi_1-xY_xO₃的掺杂形成能,发现Y替代Sr能形成更稳定的结构. 对Sr_1-xY_xTiO₃（x=0, 0125, 025, 033） 的结构进行了优化,结果表明Y替代Sr后, 随着掺杂浓度增大, 体系的晶格常数逐渐减小, 稳定性逐渐增强. 对不同掺杂浓度的Sr_1-xY_xTiO₃能带结构的计算结果表明：纯净的SrTiO₃是绝缘体, 价带顶在R点, 导带底在Γ点, 费米能级处于价带顶; 掺杂Y后, 费米能级进入到导带底中, 体系呈金属性;掺杂浓度越大,费米能级进入导带的位置越深,禁带宽度也近似变宽. 关键词： 3')" href="#">SrTiO₃ 电子结构 掺杂 VASP     

La2-xNdxCuO4+δ(0.1≤x≤1.2)体系中滞弹性弛豫与相变内耗研究

通过对La_2-xNd_xCuO_4+δ(0.1≤x≤1.2)体系中滞弹性弛豫与相变内耗性能的研究发现,当0.1≤x≤1.0时,在250K左右存在一个与间隙氧有关的弛豫内耗峰,并且当0.1≤x≤0.4时,弛豫内耗峰峰高随着x值的增大而升高,此时体系为正交结构;当0.5≤x≤1.0时,体系在宏观上呈现四方结构,此时内耗峰峰高随着x< 关键词： 2-xNd_<i>xCuO_4+δ')" href="#">La_2-xNd_<i>xCuO_4+δ 间隙氧 弛豫内耗峰 相变内耗峰     

NiS2-xSex在x=1.00附近的反铁磁量子相变

针对NiS_2-xSe_x系统在x=1.0０附近发生的反铁磁量子相变,制备了一系列NiS_2-xSe_x(x=0.96, 0.98, 1.00, 1.05, 1.10和1.20)多晶样品,对其结构、磁性质和电阻率进行了系统的观测.结果发现：样品磁化率-温度关系呈现典型的强关联电子系统特征;与铜氧化物超导体相类似,它们的电阻率-温度关系在很宽的温 关键词： 量子相变 反铁磁自旋涨落 2-xSe_x体系')" href="#">NiS_2-xSe_x体系     

应变Ge/Si1-xGex 价带色散模型

基于k·p微扰理论, 通过引入应变哈密顿量作为微扰, 建立了双轴应变Ge/Si_1-xGe_x价带色散关系模型. 模型适于任意晶向弛豫Si_1-xGe_x虚衬底上的应变Ge价带结构, 通过该模型可获得任意k方向应变Ge的价带结构和空穴有效质量. 模型的Matlab模拟结果显示, 应变Ge/Si_1-xGe_x价带带边空穴有效质量随Ge组分的增加而减小, 其各向异性比弛豫Ge更加显著. 本文研究成果对Si基应变Ge MOS器件及集成电路的沟道应力与晶向的设计有参考价值.     

应变Si电子电导有效质量模型

采用K·P微扰法建立了应变Si导带能谷由纵、横向有效质量表征的E-k关系,并在此基础上,研究分析了(001),(101),(111)晶面应变Si电子的电导有效质量与应力、能谷分裂能及晶向的关系.结果表明,弛豫Si_1-xGe_x材料(001)面生长的应变Si沿[100],[010]晶向的电子电导有效质量和弛豫Si_1-xGe_x材料(101)面生长的应变Si 关键词： 应变Si K·P法 电导有效质量     

Hole subband non-parabolicities in strained Si/Si1 − xGexquantum wells

We study the hole subband non-parabolicities in undoped pseudomorphic Si/Si_{1 − x}Ge_xquantum wells, strained in the growth direction 100. We solve exactly the multiband effective mass equation that describes the heavy, light and split-off hole valence bands. The symmetries of the Luttinger–Kohn Hamiltonian of the system are used to decouple the degenerate subbands. We calculate the in-plane dispersion relations, investigate the importance of the inclusion of the split-off hole valence band in the Hamiltonian and comment on the resulted non-parabolicities. Resonance states are also obtained.     

Strained and strain-relaxed epitaxial Ge1-xSnx alloys on Si（100） substrates

Epitaxial Ge1-xSnx alloys are grown separately on a Ge-buffer/Si(100) substrate and directly on a Si(100) substrate by molecular beam epitaxy (MBE) at low temperature. In the case of the Ge buffer/Si(100) substrate, a high crystalline quality strained Ge0.97Sn0.03 alloy is grown, with a χmin value of 6.7% measured by channeling and random Rutherford backscattering spectrometry (RBS), and a surface root-mean-square (RMS) roughness of 1.568 nm obtained by atomic force microscopy (AFM). In the case of the Si(100) substrate, strain-relaxed Ge0.97Sn0.03 alloys are epitaxially grown at 150°C-300°C, with the degree of strain relaxation being more than 96%. The X-ray diffraction (XRD) and AFM measurements demonstrate that the alloys each have a good crystalline quality and a relatively flat surface. The predominant defects accommodating the large misfit are Lomer edge dislocations at the interface, which are parallel to the interface plane and should not degrade electrical properties and device performance.     

Stokes shift in one-side modulation-n-doped-strained GaxIn1 − xAs/InP asymmetric quantum well

The effects of strain on the Stokes shift in one-side modulation-dopedGa_xIn_1 − xAs /InP asymmetric quantum wells (AQWs) are systematically investigated. By making use of a self-consistent Poisson–Schrödinger solver in the frame of a finite difference method, the quasi-Fermi levels and the band bending are determined under the effective mass approximation. The central-zone valence-band structures for compressively strained and tensile strained AQWs were calculated by making use of a four-band Luttinger–Kohn Hamiltonian. It was found that the strain influences the relative positions of the heavy-hole HH₁and the light-hole LH₁subbands and that the Stokes shifts are greatly reduced by tensile strain in the case of a Ga_0.6In_0.4As /InP AQW. Moreover, it was found that due to the presence of the two-dimensional electron gas the Stokes shifts in AQWs are much larger than the corresponding ones for a square quantum well. Also, the variation of the Stokes shift with spacer layer width for compressively strained AQWs was found to be more rapid than that for tensile strained AQWs.     

Calculation of band structure in (101)-biaxially strained Si

The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of (101)-biaxially strained Si on relaxed Si_1−X Ge _X alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys (δ₄) splitting from the [0±10] valley (Δ₂) constitute the conduction band (CB) edge, that valence band (VB) edge degeneracy is partially lifted and that the electron mass is unaltered under strain while the hole mass decreases in the [100] and [010] directions. In addition, the fitted dependences of CB splitting energy, VB splitting energy and indirect bandgap on X are all linear. Supported by the National Pre-research Foundation of China (Grant Nos. 51308040203 and 51408061105DZ0171)