Hole mobility changes under uniaxial and combinational stress in different directions are characterized and analyzed by applying additive mechanical uniaxial stress to bulk Si and SiGe-virtual-substrate-induced strain...Hole mobility changes under uniaxial and combinational stress in different directions are characterized and analyzed by applying additive mechanical uniaxial stress to bulk Si and SiGe-virtual-substrate-induced strained- Si（s-Si）p-MOSFETs（metal-oxide-semiconductor field-effect transistors）along 110 and 100 channel directions. In bulk Si,a mobility enhancement peak is found under uniaxial compressive strain in the low vertical field.The combination of 100 direction uniaxial tensile strain and substrate-induced biaxial tensile strain provides a higher mobility relative to the 110 direction,opposite to the situation in bulk Si.But the combinational strain experiences a gain loss at high field,which means that uniaxial compressive strain may still be a better choice.The mobility enhancement of SiGe-induced strained p-MOSFETs along the 110 direction under additive uniaxial tension is explained by the competition between biaxial and shear stress.展开更多
文章采用密度泛函理论方法,研究二维MoX_(2)/MgPSe_(3)(X=S、Se)异质结的电子结构和光学性能。能带结构和态密度分析发现,MoSe_(2)/MgPSe_(3)和MoSSe/MgPSe_(3)_Ⅱ具有显著的Ⅱ型能带结构,并且该异质结的导带底(conduction band minimum...文章采用密度泛函理论方法,研究二维MoX_(2)/MgPSe_(3)(X=S、Se)异质结的电子结构和光学性能。能带结构和态密度分析发现,MoSe_(2)/MgPSe_(3)和MoSSe/MgPSe_(3)_Ⅱ具有显著的Ⅱ型能带结构,并且该异质结的导带底(conduction band minimum,CBM)和价带顶(valence band maximum,VBM)分别在水的氧化还原电势(-4.44、-5.67 eV)两侧,该能带结构有利于该材料在光催化析氢方面的应用。通过对MoX_(2)/MgPSe_(3)施加均一的双轴应力,发现双轴应变对MoX_(2)/MgPSe_(3)的带隙有明显的线性调控作用,线性调控作用在压变传感方面有应用价值。光吸收系数的计算发现,MoSSe/MgPSe_(3)在紫外光区域的吸收强度相比较单独的MgPSe_(3)和MoX_(2)有显著的提高,说明异质结对于改善材料的光学性能具有重要作用。展开更多
InGaN因其可调直接带隙的物理性质被广泛应用于发光器件和太阳能电池领域,高质量生长高In组分InGaN以提高器件性能一直是研究热点。应用第一性原理方法研究了双轴应变对GaN(0001)表面In原子的吸附和扩散的影响。计算结果表明,拉伸应变...InGaN因其可调直接带隙的物理性质被广泛应用于发光器件和太阳能电池领域,高质量生长高In组分InGaN以提高器件性能一直是研究热点。应用第一性原理方法研究了双轴应变对GaN(0001)表面In原子的吸附和扩散的影响。计算结果表明,拉伸应变和压缩应变下,In原子的物理行为发生显著变化并且呈现不同特性。研究结果为深入理解双轴应变对InGaN生长的影响提供了理论基础,并且为高质量生长In Ga N提供理论指导。展开更多
As a single-phase multiferroic material, Fe3O4 exhibits spontaneous ferroelectric polarization below 38 K. However, the nature of the ferroelectricity in Fe3O4and effect of external disturbances such as strain on it r...As a single-phase multiferroic material, Fe3O4 exhibits spontaneous ferroelectric polarization below 38 K. However, the nature of the ferroelectricity in Fe3O4and effect of external disturbances such as strain on it remains ambiguous. Here, the spontaneous ferroelectric polarization of low-temperature mon- oclinic Fe3O4 was investigated by first-principles calculations. The pseudo-centrosymmetric FeB42- FEB43 pair has a different valence state. The noncentrosymmetric charge distribution results in fer- roelectric polarization. The initial ferroelectric polarization direction is in the -x and -z directions. The ferroelectricity along the y axis is limited owing to the symmetry of the Cc space group. Both the ionic displacement and charge separation at the FeB42-FeB43 pair are affected by strain, which further influences the spontaneous ferroelectric polarization of monoclinic Fe3O4. The ferroelectric polarization along the z axis exhibits an increase of 45.3% as the strain changes from 6% to -6%.展开更多
Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO i...Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is su- perior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majority- spin A1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin A1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin Al state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance （TMR） value under large biaxial strain. This work reveals the internal mechanism for the state coupling al strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel .junctions with high tunneling magnetoresistance effect.展开更多
Hexagonal GaN epilayer grown on sapphire substrate by metal organic chemical vapour deposition （MOCVD） is studied using Raman scattering and photoluminescence in a temperature range from 100K to 873 K. The model of ...Hexagonal GaN epilayer grown on sapphire substrate by metal organic chemical vapour deposition （MOCVD） is studied using Raman scattering and photoluminescence in a temperature range from 100K to 873 K. The model of strain （stress） induced by the different lattice parameters and thermal coefficients of epilayer and substrate as a function of temperature is set up. The frequency and the linewidth of E2^high mode in a GaN layer are modelled by a theory with considering the thermal expansion of the lattice, a symmetric decay of the optical phonons, and the strain （stress） in the layer. The temperature-dependent energy shift of free exeiton A is determined by using Varshni empirical relation, and the effect of strain （stress） is also investigated. We find that the strain in the film leads to a decreasing shift of the phonon frequency and an about 10meV-inereasing shift of the energy in a temperature range from 100 K to 823 K.展开更多
利用密度泛函理论(density function theory,DFT)模拟计算了二维Ⅳ-Ⅵ硫族化合物(MXs:SnS、SnSe、SnTe、GeS、GeSe和GeTe)的本征结构和电子特性,重点研究了双轴应变对MXs的能带结构特点、带隙大小和费米能级的影响。发现应变对单层MXs...利用密度泛函理论(density function theory,DFT)模拟计算了二维Ⅳ-Ⅵ硫族化合物(MXs:SnS、SnSe、SnTe、GeS、GeSe和GeTe)的本征结构和电子特性,重点研究了双轴应变对MXs的能带结构特点、带隙大小和费米能级的影响。发现应变对单层MXs的色散关系影响不大,但是对带隙大小的影响较大,而且压缩应变对带隙的影响大于拉伸应变。同时应变还可以调节GeSe、GeTe、SnSe和SnTe的直接带隙与间接带隙之间的转换。在应变的作用下单层MXs的费米能级随应变系数ε值的增加而降低,且压缩应变的影响大于拉伸应变的影响。采用应变工程研究二维MXs电子特性的变化趋势能为下一步实验上设计出高性能的二维半导体器件提供理论依据。展开更多
基金supported by the National Natural Science Foundation of China(Nos.60636010,60820106001)
文摘Hole mobility changes under uniaxial and combinational stress in different directions are characterized and analyzed by applying additive mechanical uniaxial stress to bulk Si and SiGe-virtual-substrate-induced strained- Si（s-Si）p-MOSFETs（metal-oxide-semiconductor field-effect transistors）along 110 and 100 channel directions. In bulk Si,a mobility enhancement peak is found under uniaxial compressive strain in the low vertical field.The combination of 100 direction uniaxial tensile strain and substrate-induced biaxial tensile strain provides a higher mobility relative to the 110 direction,opposite to the situation in bulk Si.But the combinational strain experiences a gain loss at high field,which means that uniaxial compressive strain may still be a better choice.The mobility enhancement of SiGe-induced strained p-MOSFETs along the 110 direction under additive uniaxial tension is explained by the competition between biaxial and shear stress.
文摘文章采用密度泛函理论方法,研究二维MoX_(2)/MgPSe_(3)(X=S、Se)异质结的电子结构和光学性能。能带结构和态密度分析发现,MoSe_(2)/MgPSe_(3)和MoSSe/MgPSe_(3)_Ⅱ具有显著的Ⅱ型能带结构,并且该异质结的导带底(conduction band minimum,CBM)和价带顶(valence band maximum,VBM)分别在水的氧化还原电势(-4.44、-5.67 eV)两侧,该能带结构有利于该材料在光催化析氢方面的应用。通过对MoX_(2)/MgPSe_(3)施加均一的双轴应力,发现双轴应变对MoX_(2)/MgPSe_(3)的带隙有明显的线性调控作用,线性调控作用在压变传感方面有应用价值。光吸收系数的计算发现,MoSSe/MgPSe_(3)在紫外光区域的吸收强度相比较单独的MgPSe_(3)和MoX_(2)有显著的提高,说明异质结对于改善材料的光学性能具有重要作用。
文摘InGaN因其可调直接带隙的物理性质被广泛应用于发光器件和太阳能电池领域,高质量生长高In组分InGaN以提高器件性能一直是研究热点。应用第一性原理方法研究了双轴应变对GaN(0001)表面In原子的吸附和扩散的影响。计算结果表明,拉伸应变和压缩应变下,In原子的物理行为发生显著变化并且呈现不同特性。研究结果为深入理解双轴应变对InGaN生长的影响提供了理论基础,并且为高质量生长In Ga N提供理论指导。
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 51671142 and U1632152） and the Key Project of the Natural Science Foundation of Tianjin City （Grant No. 16JCZDJC37300）.
文摘As a single-phase multiferroic material, Fe3O4 exhibits spontaneous ferroelectric polarization below 38 K. However, the nature of the ferroelectricity in Fe3O4and effect of external disturbances such as strain on it remains ambiguous. Here, the spontaneous ferroelectric polarization of low-temperature mon- oclinic Fe3O4 was investigated by first-principles calculations. The pseudo-centrosymmetric FeB42- FEB43 pair has a different valence state. The noncentrosymmetric charge distribution results in fer- roelectric polarization. The initial ferroelectric polarization direction is in the -x and -z directions. The ferroelectricity along the y axis is limited owing to the symmetry of the Cc space group. Both the ionic displacement and charge separation at the FeB42-FeB43 pair are affected by strain, which further influences the spontaneous ferroelectric polarization of monoclinic Fe3O4. The ferroelectric polarization along the z axis exhibits an increase of 45.3% as the strain changes from 6% to -6%.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0400801)the National Natural Science Foundation of China(Grant Nos.61774128,61674124,11604275,11304257,and 61227009)+1 种基金the Natural Science Foundation of Fujian Province of China(Grant Nos.2017J01012,2014J01026,2016J01037,and 2015J01028)the Fundamental Research Funds for the Central Universities,China(Grant Nos.20720150027,20720160044,20720160122,20720170085,20720170012,and 20720150033)
文摘Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is su- perior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majority- spin A1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin A1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin Al state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance （TMR） value under large biaxial strain. This work reveals the internal mechanism for the state coupling al strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel .junctions with high tunneling magnetoresistance effect.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 50405025 and 50535030)Program for New Century Excellent Talents in University, China
文摘Hexagonal GaN epilayer grown on sapphire substrate by metal organic chemical vapour deposition （MOCVD） is studied using Raman scattering and photoluminescence in a temperature range from 100K to 873 K. The model of strain （stress） induced by the different lattice parameters and thermal coefficients of epilayer and substrate as a function of temperature is set up. The frequency and the linewidth of E2^high mode in a GaN layer are modelled by a theory with considering the thermal expansion of the lattice, a symmetric decay of the optical phonons, and the strain （stress） in the layer. The temperature-dependent energy shift of free exeiton A is determined by using Varshni empirical relation, and the effect of strain （stress） is also investigated. We find that the strain in the film leads to a decreasing shift of the phonon frequency and an about 10meV-inereasing shift of the energy in a temperature range from 100 K to 823 K.
文摘利用密度泛函理论(density function theory,DFT)模拟计算了二维Ⅳ-Ⅵ硫族化合物(MXs:SnS、SnSe、SnTe、GeS、GeSe和GeTe)的本征结构和电子特性,重点研究了双轴应变对MXs的能带结构特点、带隙大小和费米能级的影响。发现应变对单层MXs的色散关系影响不大,但是对带隙大小的影响较大,而且压缩应变对带隙的影响大于拉伸应变。同时应变还可以调节GeSe、GeTe、SnSe和SnTe的直接带隙与间接带隙之间的转换。在应变的作用下单层MXs的费米能级随应变系数ε值的增加而降低,且压缩应变的影响大于拉伸应变的影响。采用应变工程研究二维MXs电子特性的变化趋势能为下一步实验上设计出高性能的二维半导体器件提供理论依据。
