横向约束SiGe纳米条带中的流体静力应变增强
Hydrostatic strain enhancement in laterally confined SiGe nanostripes
摘要：
SiGe纳米结构中的应变工程是纳米级光电子器件设计的基础。在这里，我们探索了一种新的策略，SiGe结构的横向限制的Si衬底，以获得高的拉伸应变，避免使用外部应力源，从而提高可扩展性。利用光谱显微镜技术、有限元模拟和从头算方法研究了横向受限富锗SiGe纳米带的应变状态。应变信息通过尖端增强拉曼光谱获得，具有前所未有的约30 nm的横向分辨率。纳米条带表现出较大的拉伸静水应变分量，其在顶部自由表面的中心处最大，并且在边缘处变得非常小。最大晶格变形大于热弛豫Ge/Si（001）层的典型值。这种应变增强源于面外方向上的受抑弛豫，这是由衬底侧壁引起的横向限制和SiGe/Si界面处（001）平面中失配应变的塑性弛豫的组合引起的。这种拉伸晶格变形在条纹表面的效果探测功函数映射，使用X-射线光电子发射显微镜的空间分辨率优于100 nm。纳米条纹表现出积极的功函数位移相对于体硅锗合金，定量证实了拉伸应变配置的电子结构计算。本研究结果对纳米尺度下光电子器件的设计具有潜在的影响。
英文摘要：
Strain-engineering in SiGe nanostructures is fundamental for the design of optoelectronic devices at the nanoscale. Here we explore a new strategy, where SiGe structures are laterally confined by the Si substrate, to obtain high tensile strain avoiding the use of external stressors, and thus improving the scalability. Spectro-microscopy techniques, finite element method simulations and ab initio calculations are used to investigate the strain state of laterally confined Ge-rich SiGe nano-stripes. Strain information is obtained by tip enhanced Raman spectroscopy with an unprecedented lateral resolution of ~ 30 nm. The nano-stripes exhibit a large tensile hydrostatic strain component, which is maximum at the center of the top free surface, and becomes very small at the edges. The maximum lattice deformation is larger than the typical values of thermally relaxed Ge/Si(001) layers. This strain enhancement originates from a frustrated relaxation in the out-of-plane direction, resulting from the combination of the lateral confinement induced by the substrate side walls and the plastic relaxation of the misfit strain in the (001) plane at the SiGe/Si interface. The effect of this tensile lattice deformation at the stripe surface is probed by work function mapping, performed with a spatial resolution better than 100 nm using X-ray photoelectron emission microscopy. The nano-stripes exhibit a positive work function shift with respect to a bulk SiGe alloy, quantitatively confirmed by electronic structure calculations of tensile strained configurations. The present results have a potential impact on the design of optoelectronic devices at a nanometer length scale.
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