生长在Si(001)衬底上应变合金层GexSi1-x的光学性质

采用经验的紧束缚方法对生长在Si(001)衬底上的应变合金Ge_xSi_1-x的光学常数进行了计算。应变对电子能带结构的影响,通过紧束缚参数随键角方向余弦的变化以及键长按经验的标度定则的变化而进行计算。其中标度指数根据对Ge和Si的畸变势常数的实验值进行拟合而确定。计算介电常数虚部时出现的动量矩阵元,根据对Ge和Si的介电常数虚部的实验曲线拟合而决定。列出了当x=0.2和1时的光学常数——介电常数虚部ε₂、折射率n、吸收系数α和反射率R的计算结

OPTICAL PROPERTIES OF COHERENTLY STRAINED ALLOYS GexSi1-x ON Si (001) SUBSTRATES

The optical constants were calculated for coherently strained alloys Ge_xSi_1-x on Si (001) substrates with tight - binding method. The effects of strains on the electronic energy band structures are taken into account by modifying the tight-binding parameters according to the variations of the bond angle cosines and the bond lengths. For the changes of the bond lengths, an empirical scaling rule is used, in which the scaling indexes are determined through fitting the calculated values of deformation potential constants to their experimental values for Ge and Si. The momentum matrix elements in the formula for calculating the imaginary part of dielectric constants are determined by fitting the ε₂ of Ge and Si. The calculated results for the optical constants , including the imaginary part of dielectric constant, the refractive index, the absorptance and the reflectance, are given both for the strained alloys and bulk alloys Ge_xSi_1-x as x=0.2 and 1. By comparison of them, the effects of strains on the optical constants are discussed.