Ge_xSi_(1-x)/Si超晶格的X射线小角衍射分析

SMALL-ANGLE X-RAY DIFFRACTION ANALYSIS OF Ge_rSi_(1-x)/Si SUPERLATTICE

用分子束外延生长了23周期的Ge_xSi_(1-x)/Si超晶格,用计算机控制的衍射仪(Cu K_α辐射)测量了X射线衍射曲线,共观察到13级超晶格结构的衍射峰。超晶格的周期和Ge平均含量可以根据考虑折射修正的布喇格定律得出。用光学多层膜反射理论分析衍射曲线可以确定超晶格的结构参数,第2级衍射峰与第一级峰的强度比对应于超晶格两种材料的相对厚度变化非常灵敏,通过比较实验和计算的I_2/I-1值,可以确定Si,Ge_xSi_(1-x)层的厚度以及合金组份x。用光学多层膜反射理谁计算得到的衍射曲线与实验曲线趋于一致。

The Ge_xSi_(1-x)/Si superlattice with 23 periods was grown by molecular beam epitaxy. The X-ray diffraction pattern was measured using a computer-controlled X-ray diffractometer with Cu K_a radiation. Interference peaks due to the superlattice structure were observed up to the 13th order. The superlattice period and the Ge average composition can be determined from the interference peak angles based on a modified Bragg's law, which was derived by including the X-ray refraction at the superlattice surface and interfaces. The structural parameter can be determined by analyzing the X-ray diffraction pattern based on the optical multilayer reflection theory. The intensity ratio of the 2nd peak to the 1st peak is quite sensitive to the variation of the thickness ratio of the two components. By comparing the calculated value of I2/I1 to the experiment, we can determine the thicknesses of Si and Ge_x si_(1-x) layers, and finallv x. The diffraction pattern calculated using the optical mutilayer reflection theory was in accordance with the measured ones.