Critical point for electron-hole droplets in strained Ge and Si

For Ge and Si under a high uniaxial stress, the split valence bands become non-parabolic. The effect of the non-parabolicity on the critical point of the electron-hole droplet in Ge(111) and Si(100) is investigated. The ground state properties of the droplet are also calculated.     

Electron-hole droplets in strained Ge and Si

The effect of the non-parabolicity of the valence band on the electron-hole droplets in Si and Ge under a large uniaxial stress is discussed. It is found that this stress-induced band feature helps to lower the ground state energy of the droplet relative to that of the free excitons.     

Hetero-Epitaxy and Self-Adaptive Stressor Based on Freestanding Fin for the 10 nm Node and Beyond

A promising technology named epitaxy on nano-scale freestanding fin(ENFF) is firstly proposed for heteroepitaxy This technology can effectively release total strain energy and then can reduce the probability of generating mismatch dislocations. Based on the calculation, dislocation defects can be eliminated completely when the thickness of the Si freestanding fin is less than 10 nm for the epitaxial Ge layer. In addition, this proposed ENFF process can provide sufficient uniaxial stress for the epitaxy layer, which can be the major stressor for the SiGe or Ge channel fin field-effect transistor or nanowire at the 10 nm node and beyond. According to the results of technology computer-aided design simulation, nanowires integrated with ENFF show excellent electrical performance for uniaxial stress and band offset. The ENFF process is compatible with the state of the art mainstream technology, which has a good potential for future applications.     

Disappearance of Be-related photoluminescence in Be-doped Ge under large uniaxial stresses

Increasing uniaxial stress applied to Ge doped with the double acceptor Be results in the disappearance of first the luminescence due to two-exciton complexes bound to Be, and at a higher stress the Be bound exciton itself, with a concomitant increase in free exciton intensity by a factor of 25. These results can be readily understood in terms of the shell model of excitonic complexes. Similar lines observed in Zn-doped Ge behave in a qualitatively different way under uniaxial stress, indicating that the existing model for the origin of the Zn lines must be modified.     

纳米尺度下Si/Ge界面应力释放机制的分子动力学研究

采用分子动力学方法研究了纳米尺度下硅(Si)基锗(Ge)结构的Si/Ge界面应力分布特征,以及点缺陷层在应力释放过程中的作用机制.结果表明:在纳米尺度下, Si/Ge界面应力分布曲线与Ge尺寸密切相关,界面应力下降速度与Ge尺寸存在近似的线性递减关系;同时,在Si/Ge界面处增加一个富含空位缺陷的缓冲层,可显著改变Si/Ge界面应力分布,在此基础上对比分析了点缺陷在纯Ge结构内部引起应力变化与缺陷密度的关系,缺陷层的引入和缺陷密度的增加可加速界面应力的释放.参考对Si/Ge界面结构的研究结果,可在Si基纯Ge薄膜生长过程中引入缺陷层,并对其结构进行设计,降低界面应力水平,进而降低界面处产生位错缺陷的概率,提高Si基Ge薄膜质量,这一思想在研究报道的Si基Ge膜低温缓冲层生长方法中初步得到了证实.     

Interplay of surface morphology, strain relief, and surface stress during surfactant mediated epitaxy of Ge on Si

Lattice-mismatch-induced surface or film stress has significant influence on the morphology of heteroepitaxial films. This is demonstrated using Sb surfactant-mediated epitaxy of Ge on Si(111). The surfactant forces a two-dimensional growth of a continous Ge film instead of islanding. Two qualitatively different growth regimes are observed. Elastic relaxation: Prior to the generation of strain-relieving defects the Ge film grows pseudomorphically with the Si lattice constant and is under strong compressive stress. The Ge film relieves strain by forming a rough surface on a nm scale which allows partial elastic relaxation towards the Ge bulk lattice constant. The unfavorable increase of surface area is outbalanced by the large decrease of strain energy. The change of film stress and surface morphology is monitored in situ during deposition at elevated temperature with surface stress-induced optical deflection and high-resolution spot profile analysis low-energy electron diffraction. Plastic relaxation: After a critical thickness the generation of dislocations is initiated. The rough phase acts as a nucleation center for dislocations. On Si(111) those misfit dislocations are arranged in a threefold quasi periodic array at the interface that accommodate exactly the different lattice constants of Ge and Si. Received: 1 April 1999 / Accepted: 17 August 1999 / Published online: 6 October 1999     

第一性原理研究[112]硅锗异质结纳米线的电子结构与光学性质

基于密度泛函理论体系下的广义梯度近似,本文利用第一性原理方法着重研究了[112]晶向硅锗异质结纳米线的电子结构与光学性质.能带结构计算表明:随着锗原子数的增加,[112]晶向硅锗纳米线的带隙逐渐减小;对Si_(36)Ge_(24)H_(32)纳米线施加单轴应变,其能量带隙随拉应变的增加而单调减小.光学性质计算则表明:随着锗原子数的增加,[112]硅锗纳米线介电函数的峰位和吸收谱的吸收边均向低能量区移动;而随着拉应变的增大,吸收系数峰值呈现出逐渐减小的趋势,且峰位不断向低能量区移动,上述结果说明锗原子数的增加与施加拉应变均导致[112]硅锗纳米线的吸收谱产生红移.本文的研究为硅锗异质结纳米线光电器件研究与设计提供一定的理论参考.     

Sign reversals of charge on electron-hole drop

The first self-consisted calculation of surface properties of electron-hole drop (EHD) in Ge is reported. It is predicted that in Ge under <111> uniaxial stress the sign of charge on EHD will undergo two sign reversals; at zero stress the charge on EHD is negative, becomes positive at intermediate stress (? 3 kg mm^-2), and then reverses to negative at very large stress. Values of surface energy and dipole layer are given.     

Hole mobility enhancement in uniaxial stressed Ge dependence on stress and transport direction

Utilizing a six-band k.p valence band calculations that considered a strained perturbation Hamiltonian, uniaxial stress-induced valence band structure parameters for Ge such as band edge energy shift, split, and effective mass were quantitatively evaluated. Based on these valence band parameters, the dependence of hole mobility on uniaxial stress (direction, type, and magnitude) and hole transport direction was theoretical studied. The results show that the hole mobility had a strong dependence on the transport direction and uniaxial stress. The hole mobility enhancement can be found for all transport directions and uniaxial stess configurations, and the hole transport along the [110] direction under the uniaxial [110] compressive stress had the highest mobility compared to other transport directions and stress configurations.     

3D composition of epitaxial nanocrystals by anomalous X-ray diffraction: observation of a Si-rich core in Ge domes on Si(100)

Three-dimensional composition maps of nominally pure Ge domes grown on Si(001) at 600 degrees C were obtained from grazing incidence anomalous x-ray scattering data at the Ge K edge. The data were analyzed in terms of a stack of layers with laterally varying concentration. The results demonstrated that the domes contained a Si-rich core covered by a Ge-rich shell and were independently supported by selective etch experiments. The composition profile resulted from substrate Si alloying into the Ge during growth to partially relax the stress in and under the domes.     

Magneto-piezospectroscopy of acceptors in tetrahedrally coordinated semiconductors

This paper presents a study of the magnetospectroscopy of acceptors in elemental group-IV semiconductors in the presence of uniaxial stress. We use a formulation of the effect of stress on the transition probabilities for optical absorption which represents a considerable simplification over previous treatments. We give an analysis of both the longitudinal and the transverse magneto-spectroscopy of acceptors in semiconductors having the diamond structure under uniaxial stress. The results are used to determine the values of theg-factors for two levels of Ga acceptors in Ge by comparing the present results with the experimental data. Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction.     

Ge(5 × 5) as a wetting layer on Si(1 1 1)

Ab initio total energy methods are used to investigate the effects on a Ge(1 1 1)-5 × 5 surface of the lateral compressive stress that would be due to a Si substrate, and the effects of intermixing at the interface with the substrate. The effects of stress due to the lattice mismatch between Si and Ge are studied on a Ge slab by changing the lattice constant in the surface plane from that of experimental bulk diamond Ge to that of Si. When this is done the height difference of the Ge adatoms in the faulted half-cell from those in the unfaulted half is accentuated. Effects on the Ge surface due to the presence of the Si-Ge interface were studied using a thin Ge layer on a Si substrate. The presence of the substrate leads to corrugations with significant height differences appearing among the faulted adatoms. The energetics of intermixing were investigated for Si-Ge single atom interchanges. Additional corrugations resulted from the shortened bondlengths due to the Si impurity in the wetting layer.     

[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     

Calculation of shuffle 60° dislocation width and Peierls barrier and stress for semiconductors silicon and germanium

The dislocation width for shuffle 60° dislocation in semiconductors Si and Ge have been calculated by the improved P-N theory in which the discrete effect has been taken into account. Peierls barrier and stress have been evaluated with considering the contribution of strain energy. The discrete effect make dislocation width wider, and Peierls barrier and stress lower. The dislocation width of 60° dislocation in Si and Ge is respectively about 3.84 Å and 4.00 Å (～1b, b is the Burgers vector). In the case of 60° dislocation, after considering the contribution of strain energy, Peierls barrier and stress are increased. The Peierls barrier for 60° dislocation in Si and Ge is respectively about 15 meV/Å and 12–14 meV/Å, Peierls stress is about 3.8 meV/ų (0.6 GPa) and 2.7–3.3 meV/ų (0.4–0.5 GPa). The Peierls stress for Si agrees well with the numerical results and the critical stress at 0 K extrapolated from experimental data. Ge behaves similarly to Si.     

Flow pattern defects in germanium-doped Czochralski silicon crystals

The distribution and etching rate of flow pattern defects (FPDs) in germanium- doped Czochralski (GCZ) silicon (Si) wafers with light and heavy dopants—either boron (B) or phosphorus (P)—have been investigated. In the lightly doped (both B and P) Czochralski (CZ) Si crystals, the FPD densities in GCZ Si decrease with the increase of Ge concentration. In the heavily B-doped GCZ Si crystals, the FPDs are denser compared with the heavily B-doped CZ Si, whereas the reverse is true in the heavily P-doped GCZ Si and CZ Si crystals. It is also shown that the etching rates in the lightly doped CZ Si crystals can be slightly enlarged by the Ge doping. It is proposed that, in lightly doped GCZ Si, Ge doping could consume free vacancies and thus form high-density but small-sized voids, while the stress compensation induced by B and Ge atoms could increase the vacancy concentration in heavily B-doped GCZ Si, leading to sparse and large-sized voids.     

Electronic structure of semiconducting crystals under high stress

We present a calculation of the band structure of semiconducting crystals under arbitrarily high stress, in which all input parameters are determined from the properties of the unstressed crystal alone. The method is applied to obtain the band structure of Ge and Si at high stress, and the strain dependence of the energies and matrix elements of a number of critical-point transitions are presented.     

Direct mapping of strain in a strained silicon transistor by high-resolution electron microscopy

Aberration-corrected high-resolution transmission electron microscopy (HRTEM) is used to measure strain in a strained-silicon metal-oxide-semiconductor field-effect transistor. Strain components parallel and perpendicular to the gate are determined directly from the HRTEM image by geometric phase analysis. Si80Ge20 source and drain stressors lead to uniaxial compressive strain in the Si channel, reaching a maximum value of -1.3% just below the gate oxide, equivalent to 2.2 GPa. Strain maps obtained by linear elasticity theory, modeled with the finite-element method, agree with the experimental results to within 0.1%.     

(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     

Investigation of positively charged acceptor states in Si and Ge under uniaxial stress by phonon induced conduction

We use superconducting Al-tunnel junctions as tunable phonon generators in the meV-range to determine ground state splitting at zero stress of positively charged states associated with single acceptors in Si and double acceptors in Ge. From the stress and energy dependence of the conductivity induced by high frequency phonon irradiation of the corresponding two- and three-hole states we find that the splitting is below 0.1 meV for the ground states of Si:B⁺ and Ge:Be⁺, and 1 meV and 1.2 meV for Si:Ga⁺ and Si:Al⁺, respectively. These level separations are comparable to those found previously for the ground states of the corresponding acceptor bound excitons A⁰X. For the deeper acceptors Si:In⁺, Si:Tl⁺, and Ge:Zn⁺ the results are qualitatively different.     

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