不同晶系应变Si状态密度研究

应变Si技术是当前微电子领域研究发展重点,态密度是其材料的重要物理参量.本文基于应力相关KP理论,建立了(001),(101)和(111)晶面施加双轴应力形成的四方、单斜及三角晶系应变Si导带、价带态密度模型.结果表明,除单斜和三角晶系导带底态密度外,应力对其余各态密度均有显著影响.本文所得模型数据量化,可为应变Si材料物理的理解及其他物理参数模型的建立奠定重要理论基础. 关键词： 应变Si KP 态密度     

应变(001)p型金属氧化物半导体反型层空穴量子化与电导率有效质量

基于k·p微扰理论框架,研究建立了单轴张/压应变Si,Si基双轴应变p型金属氧化物半导体(PMOS)反型层空穴量子化有效质量与空穴面内电导率有效质量模型.结果表明:对于单轴应力PMOS,选择单轴压应力可有效增强器件的性能;同等增强PMOS空穴迁移率,需要施加的单轴力强度小于双轴力的强度;在选择双轴应力增强器件性能时,应优先选择应变Si1-x Ge x作为沟道材料.所获得的量化理论结论可为Si基及其他应变器件的物理理解及设计提供重要理论参考.     

[110]/(001)单轴应变Si本征载流子浓度模型

本文首先讨论了在沿[110]方向的单轴应力对体Si材料能带结构参数的影响,在此基础上计算出单轴应变Si中平衡载流子浓度,给出了物理意义明确的导带、价带有效态密度的表达式.最后,结合有效态密度和禁带宽度的表达式,建立了[110]/(001)单轴应变Si本征载流子浓度模型.本文的研究方法亦适用于建立(001)面任意应力方向上的应变Si本征载流子浓度模型,并为相关单轴应变Si器件的设计、建模以及仿真提供了一定的理论参考. 关键词： [110]/(001)单轴应变Si 有效态密度 本征载流子浓度     

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     

单轴应变Si(001)任意晶向电子电导有效质量模型

单轴应变Si材料电子电导有效质量是理解其电子迁移率增强的关键因素之一, 对其深入研究具有重要的理论意义和实用价值. 本文从Schrödinger方程出发, 将应力场考虑进来, 建立了单轴应变Si材料导带E-k解析模型. 并在此基础上, 最终建立了单轴应变Si(001)任意晶向电子电导率有效质量与应力强度和应力类型的关系模型. 本文的研究结果表明: 1) 单轴应力致电子迁移率增强的应力类型应选择张应力. 2) 单轴张应力情况下, 仅从电子电导有效质量角度考虑, [110]/(001)晶向与[100]/(001)晶向均可. 但考虑到态密度有效质量的因素, 应选择[110]/(001)晶向. 3) 沿(001)晶面上[110]晶向施加单轴张应力时, 若想进一步提高电子迁移率, 应选取[100]晶向为器件沟道方向. 以上结论可为应变Si nMOS器件性能增强的研究及导电沟道的应力与晶向设计提供重要理论依据. 关键词： 单轴应变 E-k关系')" href="#">E-k关系 电导有效质量     

四方晶系应变Si空穴散射机制

基于Fermi黄金法则及Boltzmann方程碰撞项近似理论, 推导建立了(001)弛豫Si_1-xGe_x衬底外延四方晶系应变Si空穴散射几率与应力及能量的理论关系模型, 包括离化杂质、声学声子、非极性光学声子及总散射概率(能量40 meV时)模型. 结果表明: 当Ge组分(x)低于0.2时, 应变Si/(001)Si_1-xGe_x材料空穴总散射概率随应力显著减小. 之后, 其随应力的变化趋于平缓. 与立方晶系未应变Si材料相比, 四方晶系应变Si材料空穴总散射概率最多可减小66%. 应变Si材料空穴迁移率增强与其散射概率的减小密切相关, 本文所得量化模型可为应变Si空穴迁移率及PMOS器件的研究与设计提供理论参考.     

应变Si/(001)Si1-xGex空穴有效质量各向异性

基于应变Si/(001)Si1-xGex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)Si1-xGex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,该研究成果为Si基应变PMOS器件性能增强的研究及导电沟道的应力与晶向设计提供了重要理论依据.     

非对称双轴张应变对锗能带的影响

采用第一性原理方法系统地研究了沿(001)、(101)和(111)面施加晶面内各方向应变不相等的双轴张应变,即非对称双轴张应变对锗能带结构的影响.结果表明:对于沿(001)面施加非对称双轴张应变,至少某一个方向应变大于2.95%,间接-直接带隙转变才能发生;对于沿(101)面施加非对称双轴张应变,至少某一个方向应变大于3.44%,间接-直接带隙转变才能发生;然而,沿(111)面施加非对称双轴张应变,不发生间接-直接带隙转变.另外,研究还发现无论是施加对称双轴应变还是非对称双轴应变,间接-直接带隙转变得到的应变Ge带隙值都与应变前后拉伸面面积变化大小成反比.     

(001)面任意方向单轴应变硅材料能带结构

首先计算了(001)晶面单轴应变张量,在此基础上采用结合形变势理论的K ·P微扰法建立了在(001)晶面内受任意方向的单轴压/张应力作用时,应变硅材料的能带结构与应力(类型、大小)及晶向的关系模型,进而分析了不同单轴应力(类型、大小)及晶向对应变硅材料导带带边、价带带边、导带分裂能、价带分裂能、禁带宽度的影响.研究结果可为单轴应变硅器件应力及晶向的选择设计提供理论依据. 关键词： 单轴应变硅 K ·P法 能带结构     

单轴应变SiNMOSFET源漏电流特性模型

本文在建立单轴应变Si NMOSFET迁移率模型和阈值电压模型的基础上, 基于器件不同的工作区域, 从基本的漂移扩散方程出发, 分别建立了单轴应变Si NMOSFET源漏电流模型. 其中将应力的影响显式地体现在迁移率和阈值电压模型中, 使得所建立的模型能直观地反映出源漏电流特性与应力强度的关系. 并且对于亚阈区电流模型, 基于亚阈区反型电荷, 而不是采用常用的有效沟道厚度近似的概念, 从而提高了模型的精度. 同时将所建模型的仿真结果与实验结果进行了比较, 验证了模型的可行性. 该模型已经被嵌入进电路仿真器中, 实现了对单轴应变Si MOSFET 器件和电路的模拟仿真.     

Splitting of frequencies of optical phonons in tensile-strained germanium layers

Tensile-strained germanium films in Ge/GeSn/Si/GeSnSi multilayer heterostructures grown by molecularbeam epitaxy on Si(001) substrates are investigated by Raman spectroscopy. Biaxial tensile strains in the films reach 1.5%, which exceeds values previously obtained for this system. Splitting of frequencies of long-wavelength optical phonons is experimentally observed; i.e., the shift of the frequency of the singlet induced by biaxial tensile strains is larger than the shift of the frequency of the doublet in agreement with calculations. The strain-induced shift of Raman scattering peaks from two-phonon scattering in germanium is also detected.     

Poly(vinylpyrrolidone)‐stabilized silver nanoparticles for strained‐silicon surface enhanced Raman spectroscopy

Poly(vinylpyrrolidone)‐stabilized silver nanoparticles deposited onto strained‐silicon layers grown on graded Si_1−xGe_x virtual substrates are utilized for selective amplification of the Si–Si vibration mode of strained silicon via surface‐enhanced Raman scattering spectroscopy. This solution‐based technique allows rapid, highly sensitive and accurate characterization of strained silicon whose Raman signal would usually be overshadowed by the underlying bulk SiGe Raman spectra. The analysis was performed on strained silicon samples of thickness 9, 17.5 and 42 nm using a 488 nm Ar⁺ micro‐Raman excitation source. The quantitative determination of strained‐silicon enhancement factors was also made. Copyright © 2011 John Wiley & Sons, Ltd.     

ZnSe-ZnS应变超晶格的Raman散射

本文报导了Znse—ZnS应变超晶格的Raman光学声子谱.我们观测到,随着应变大小的改变,ZnSe和ZnS的纵向光学声子发生频移.ZnSe层中纵向光学声子可发生较大的蓝移,也可发生较小的红移;ZnS层中的纵向光学声子发生较大的红移.这些现象为“应变场下的光学模理论”所解释.文中还报导了在波数为110cm-1处观测到一很强的散射峰,并把它归结为超晶格表面层单斜Se所引起的散射;在其它地方还观测到非晶态Se、三角Se引起的散射峰.     

Retarded thermal oxidation of strained Si substrate

Strained Si is recognized as a necessary technology booster for modern integrated circuit technology. However, the thermal oxidation behaviors of strained Si substrates are not well understood yet despite their importance. In this study,we for the first time experimentally find that all types of strained Si substrates(uniaxial tensile, uniaxial compressive,biaxial tensile, and biaxial compressive) show smaller thermal oxidation rates than an unstrained Si substrate. The possible mechanisms for these retarded thermal oxidation rates in strained Si substrates are also discussed.     

Si/SiGe异质结构的硅盖层中应变对Raman谱特征的影响

应变Si/SiGe异质结构通过大剂量Ge离子注入并结合高温快速热退火制备而成。325 nm波长的紫外激光被用于调查应变Si盖层的Raman谱特征。实验发现,硅盖层中的张应变导致硅的520 cm-1的一级拉曼散射峰向低频方向偏移,峰的偏移程度反映硅盖层中横向张应力的大小约为12.5×108 N·m-2。硅盖层中的张应变并未导致1 555和2 330 cm-1的次级拉曼散射峰的变化。     

The critical thickness of silicon-germanium layers grown by liquid phase epitaxy

Silicon-germanium layers are grown from metallic solution on (100) and (111) silicon substrates. On (111) Si, coherently strained dislocation-free SiGe layers are obtained with thicknesses larger than predicted by the current models of misfit-induced strain relaxation. A comprehensive characterisation by imaging, diffraction, and analytical electron microscopy techniques is carried out to determine the critical thickness, study the onset of plastic relaxation, and explain the particular growth mechanisms leading to an unexpectedly high thickness of elastically strained SiGe layers. A vertical Ge concentration gradient and the formation of step edges on the layers, where lateral strain relaxes locally, explain the high critical thickness. The model of Matthews and Blakeslee is modified in order to match the experimental observations for solution-grown SiGe layers. Received: 29 July 1999 / Accepted: 29 July 1999 / Published online: 27 October 1999     

The comparison between CdS thin films grown on Si(111) substrate and quartz substrate by femtosecond pulsed laser deposition

Two kinds of cadmium sulfate (CdS) thin films have been grown at 600 °C onto Si(111) and quartz substrates using femtosecond pulsed laser deposition (PLD). The influence of substrates on the structural and optical properties of the CdS thin films grown by femtosecond pulsed laser deposition have been studied. The CdS thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL) and Raman spectroscopy. Although CdS thin films deposited both on Si(111) and quartz substrates were polycrystalline and hexagonal as shown by the XRD , SEM and AFM results, the crystalline quality and optical properties were found to be different. The size of the grains for the CdS thin film grown on Si(111) substrate were observed to be larger than that of the CdS thin film grown on quartz substrate, and there is more microcrystalline perpendicularity of c-axis for the film deposited on the quartz substrate than that for the films deposited on the Si substrate. In addition, in the PL spectra, the excitonic peak is more intense and resolved for CdS film deposited on quartz than that for the CdS film deposited on Si(111) substrate. The LO and TO Raman peaks in the CdS films grown on Si(111) substrate and quartz substrate are different, which is due to higher stress and bigger grain size in the CdS film grown on Si(111) substrate, than that of the CdS film grown on the amorphous quartz substrate. All this suggests that the substrates have a significant effect on the structural and optical properties of thin CdS films. PACS 81.15.Fg; 81.05.Ea; 78.20.-e; 78.67.-n; 42.62.-b     

Fabrication of well-defined individual dislocations in SiGe as a novel one-dimensional system

We show a new way to fabricate well-defined individual dislocations in SiGe. We started with a fully pseudomorphic but metastable SiGe layer grown on Si(0 0 1) by molecular beam epitaxy. Next, elongated (1 mm) mesa stripes with various widths (0.5–3 μm) were fabricated by a combination of isotropic and anisotropic etching. For smaller stripes, elastic relaxation of the strained SiGe layer can occur, transforming the originally biaxial strained layer into uniaxial strained subsystems. Subsequent strain relaxation caused by high temperature treatments leads to the formation of individual dislocation along the mesa stripes. The number of parallel dislocation can be adjusted by the original strain (Si:Ge ratio and layer thickness) and the mesa widths. We were able to fabricate structures with exactly one dislocation. Finally, contact pads were added to the stripes enabling the electrical characterization of individual dislocation.