Maras E, Pizzagalli L, Ala-Nissila T, Jónsson H
COMP Center of Excellence Aalto University School of Science, FI-00076, Aalto, Espoo, Finland.
Department of Applied Physics, Aalto University School of Science, FI-00076, Aalto, Espoo, Finland.
Sci Rep. 2017 Sep 20;7(1):11966. doi: 10.1038/s41598-017-12009-y.
Understanding how edge misfit dislocations (MDs) form in a GeSi/Si(001) film has been a long standing issue. The challenge is to find a mechanism accounting for the presence of these dislocations at the interface since they are not mobile and cannot nucleate at the surface and glide towards the interface. Furthermore, experiments can hardly detect the nucleation and early stages of growth because of the short time scale involved. Here we present the first semi-quantitative atomistic calculation of the formation of edge dislocations in such films. We use a global optimization method and density functional theory calculations, combined with computations using potential energy functions to identify the best mechanisms. We show that those previously suggested are relevant only for a low film strain and we propose a new mechanism which accounts for the formation of edge dislocations at high film strain. In this one, a 60° MD nucleates as a "split" half-loop with two branches gliding on different planes. One branch belongs to the glide plane of a complementary 60° MD and therefore strongly favors the formation of the complementary MD which is immediately combined with the first MD to form an edge MD.
理解锗硅合金/硅（001）薄膜中边缘失配位错（MDs）是如何形成的，一直是个长期存在的问题。挑战在于找到一种机制来解释这些位错在界面处的存在，因为它们不可移动，且不能在表面形核并向界面滑移。此外，由于涉及的时间尺度很短，实验很难检测到位错的形核和生长早期阶段。在此，我们展示了此类薄膜中边缘位错形成的首次半定量原子计算。我们使用全局优化方法和密度泛函理论计算，并结合使用势能函数的计算来确定最佳机制。我们表明，之前提出的那些机制仅适用于低薄膜应变情况，并且我们提出了一种新机制，该机制解释了高薄膜应变下边缘位错的形成。在这种机制中，一个60°的MD作为一个“分裂”的半环形核，有两个分支在不同平面上滑移。一个分支属于互补60°MD的滑移面，因此强烈有利于互补MD的形成，该互补MD会立即与第一个MD结合形成一个边缘MD。
