COMPOSITIONAL AND STRUCTURAL CHARACTERIZATION OF STRAINED SI SIXGE1-XMULTILAYERS AND INTERFACES BY HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY/

A method is described for the quantitative characterization of straine d Si/SixGe1-x multilayers and interfaces by high-resolution transmissi on 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 DELTAf and specimen thickness t and takes tetragonal lat tice distortions fully into account. From an extensive study of the im age formation process for SixGe1-x alloys and coherent Si/SixGe1-x int erfaces, ranges of DELTAf and t were identified by Bloch-wave and mult i-slice image simulations at 400 keV for which a quasi-linear function al 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 imag e Fourier coefficients in geometrically distorted lattice images, loca l composition values x can be determined at near-atomic resolution wit h an accuracy of DELTAx less-than-or-equal-to +/- 0.1 and interface sh arpness can be detected at the atomic level. Recent applications of th e method to the characterization of interfaces of strained SixGe1-x la yers and short-period Si(m)Ge(n) superlattices fabricated by different deposition techniques will be presented.