Compositional and structural characterization of strained Si/Si x Ge1?x multilayers and interfaces by high-resolution transmission electron microscopy

Abstract

A method is described for the quantitative characterization of strained Si/SixGe1−x multilayers and interfaces by high-resolution transmission electron microscopy (HRTEM) in [110] and [100] crystal projections. The method relies on systematic variations of the image contrast with variations of the local composition x for certain ranges of objective lens defocus Δf and specimen thickness t and takes tetragonal lattice distortions fully into account. From an extensive study of the image formation process for SixGe1−x alloys and coherent Si/SixGe1−x interfaces, ranges of Δf and t were identified by Bloch-wave and multi-slice image simulations at 400 keV for which a quasi-linear functional relationship between the composition x and the first-order Fourier coefficients of the image intensity exists. By application of a novel image-processing algorithm, which allows a precise measurement of image Fourier coefficients in geometrically distorted lattice images, local composition values x can be determined at near-atomic resolution with an accuracy of Δx ≤ ±0.1 and interface sharpness can be detected at the atomic level. Recent applications of the method to the characterization of interfaces of strained SixGe1−x layers and short-period SimGen superlattices fabricated by different deposition techniques will be presented.