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利用掠入射荧光X射线吸收精细结构(XAFS)方法研究了在400℃的温度下分子束外延生长的Si/Gen/Si(001)异质结薄膜(n=1,2,4和8个原子层)中Ge原子的局域环境结构.结果表明,在1至2个Ge原子层(ML)生长厚度的异质结薄膜中,Ge原子的第一近邻配位主要是Si原子.随着Ge原子层厚度增加到4ML,Ge原子的最近邻配位壳层中的Ge-Ge配位的平均配位数增加到1.3.当Ge原子层厚度增加到8ML时,第一配位壳层中的Ge-Ge配位占的比例只有55%.这表明在400℃的生长条件下,Ge原子有很强的迁移到Si覆盖层的能力.随着Ge层厚度从1增加到2,4和8ML,Ge原子迁移到Si覆盖层的量由0.5ML分别增加到1.5,2.0和3.0ML.认为在覆盖Si过程中Ge原子的迁移主要是通过产生Ge原子表面偏析来降低表面能和Ge层的应变能.
The Si / Gen / Si (001) heterojunction thin films (n = 1, 2, 4 and 8 atoms) grown by molecular beam epitaxy at 400 ℃ were studied by the grazing incidence X-ray fluorescence absorption fine structure (XAFS) Layer) Ge atoms in the local environment structure.The results show that the Ge atoms in the first one to two Ge layer thickness (ML) growth heterojunction thin film, the first nearest neighbor coordination of Ge atoms Si atoms with Ge When the thickness of the atomic layer increases to 4ML, the average coordination number of Ge-Ge coordination in the nearest neighbor coordination shell of Ge atoms increases to 1.3. When the thickness of Ge atomic layer increases to 8ML, Ge-Ge ratio is only 55%, indicating that Ge atoms have a strong ability to migrate to Si capping layer at 400 ° C. As the Ge layer thickness increases from 1 to 2, 4 and 8 ML , The amount of Ge atoms migrating to the Si capping layer increased from 0.5ML to 1.5, 2.0 and 3.0ML, respectively.It is considered that the migration of Ge atoms in the process of covering Si mainly reduces the surface energy and the strain of the Ge layer by generating surface segregation of Ge atoms can.