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半导体量子点形成临界尺寸的定量预测

Quantitative prediction of critical size for the formation of semiconductor quantum dots

  • 摘要: 半导体量子点是一类具有显著量子效应的零维量子结构,自组的模型系统,表现为Stranski-Krastanov型生长.其特征为,当超过3—4个Ge单原子层(浸润层)时,则由二维层状生长转变为三维岛状生长.Ge/Si量子点是初期形成的与衬底共格无位错的三维岛,岛表面由105晶面组成.文章作者利用第一性原理计算和介观理论模拟相结合的连续式多尺度(sequential multi-scale)方法,第一次对纯Ge和GeSi合金量子点在Si(001)表面的成核临界尺寸进行了定量的理论预测,同时研究了岛边缘的应力不连续对量子点稳定性的影响,实现了对Ge/Si量子点的形成和稳定性定量的理论研究.

     

    Abstract: Semiconductor quantum dots (QDs) are often fabricated by epitaxial growth. Germanium QD formation on Si(001) is an important prototype model system for both fundamental research and practical application. Ge film grows on Si via the Stranski-Krastanov growth mode, first forming a smooth wetting layer several monolayers thick, followed by three-dimensional islanding. The originally formed 3D Ge islands are called “huts”, being coherent with the Si substrate and bounded by 105-faceted crystalline planes. By combining the first-principles calculation with continuum theoretical modeling, we prescribe a “sequential multi-scale approach” to quantitatively investigate the formation and stability of Ge QD on Si. We calculate from first-principles the surface energies, surface stresses and their strain dependence of Ge-covered Si (001) and (105) surfaces, as a function of deposited Ge layer thickness. Using these results as input parameters, we further perform continuum model calculations to quantitatively predict the critical size for Ge QD nucleation/formation and assess their thermodynamic stability. Our studies have not only elucidated the existing experimental results, but also provided new insights to understanding the physical mechanisms underlying the QD formation and self-assembly.

     

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