Depth profiles of the interfacial strains of Si0.7Ge0.3/Si using three-beam Bragg-surface diffraction.

Yan-Zong Zheng,Shih-Lin Chang,Yun-Liang Soo

doi:10.1038/srep25580

Abstract

Interfacial strains are important factors affecting the structural and physical properties of crystalline multilayers and heterojunctions, and the performance of the devices made of multilayers used, for example, in nanowires, optoelectronic components, and many other applications. Currently existing strain measurement methods, such as grazing incidence X-ray diffraction (GIXD), cross-section transmission electron microscope, TEM, and coherent diffractive imaging, CDI, are limited by either the nanometer spatial resolution, penetration depth, or a destructive nature. Here we report a new non-destructive method of direct mapping the interfacial strain of [001] Si0.7Ge0.3/Si along the depth up to ~287 nm below the interface using three-beam Bragg-surface X-ray diffraction (BSD), where one wide-angle symmetric Bragg reflection and a surface reflection are simultaneously involved. Our method combining with the dynamical diffraction theory simulation can uniquely provide unit cell dimensions layer by layer, and is applicable to thicker samples.

Highlights

Interfacial strains are important factors affecting the structural and physical properties of crystalline multilayers and heterojunctions, and the performance of the devices made of multilayers used, for example, in nanowires, optoelectronic components, and many other applications
Bragg-surface diffraction (BSD)[1,2,3,4] occurs when the sample crystal is first aligned for a symmetric Bragg reflection, say G, by adjusting the Bragg angle θB and the crystal is rotated by the azimuth, φ, around the reciprocal lattice vector g of the G-reflection, without disturbing the G reflection, to bring an additional surface reflection, L, satisfying Bragg’s law (Fig. 1a)
Since point L is on the equatorial plane, the reflected beam is propagating along the crystal surface, the grazing-exit diffraction, L, provides scattering information from the surface, interface, up to the depth comparable with the extreme depth limitation by the evanescent waves of the Bragg reflection G

Summary

Therefore a fitting function

(a) The three diagonal elements, ax, by and cz are plotted from the top (depth = 0 Å) to the thin-film, Si0.7Ge0.3 (until 597 Å), and the interface (597~750 Å), and the Si substrate. The two elements ay and x- and z-components of tahzearlaettthiceeyu-naint dvezc-tocor,m b.p(odn)eTnhtse of cx the lattice and cy are unit vector, a. (c) The bx and the x- and y- components of bz are the lattice unit vector, c. The corresponding strains, calculated according to the predicted lattice constants

Author Contributions

Additional Information