Strain mapping of ultrathin epitaxial ZnTe and MnTe layers embedded in CdTe

Abstract

High-resolution electron microscopy is used to investigate the morphology of ultrathin pseudomorphic (001) ZnTe and MnTe strained layers grown in CdTe. Local distortions of the crystal lattice are measured directly on high-resolution images by use of image processing software. In the case of ZnTe/CdTe superlattices, the method yields the location of Zn within each place in the heterostructure and the total amount of Zn per period. For MnTe layers embedded in CdTe, one can deduce the atomic morphology of the interfaces which are shown to present a clear asymmetry.

Strain Measurement in Semiconductor Heterostructures by Scanning Transmission Electron Microscopy

“…can be divided in two groups-imaging and diffraction. The former originally exploits atomically resolved TEM micrographs with respect to lattice fringe distances~Bierwolf Bayle et al, 1994;Jouneau et al, 1994;Robertson et al, 1995;Rosenauer et al, 1998!. As the observed high-resolution pattern is formed by the interference of all diffracted beams passing the objective aperture, subsequent studies included partly extensive analysis of the phases of Bragg beams as a function of specimen thickness, orientation, composition, crystal potential Fourier components, lens aberrations, and defocus~Tillmann et al, 2000;Hÿtch & Plamann, 2001;Rosenauer et al, 2001;Rosenauer et al, 2006;Guerrero et al, 2007;Müller et al, 2010;Yu & Mader, 2010!. One disadvantage common to all high-resolution TEM techniques is the restricted field of view not only because the lattice fringe pattern must be sampled densely enough to measure fringe spacings precisely, but also because measured fringe distances need to be normalized tõ substrate! regions with known strain state, which may be too far away from the region of interest.…”

Magnetic Properties of Molecular Beam Epitaxy Grown High x Cd1-xMnxTe

“…As mentioned before, this indicates a decrease in Mn concentration in CdMnTe layers. Secondly, as it has been shown by high resolution electron microscopy (HREM) lattice images method [7], due to a surface diffusion lower for Mn than for Cd, CdMnTe layers do not grow uniformly. The effect leads to non-abupt interfaces which may be as wide as 7 monolayers for a 100 Α thick layers.…”

Analysis of Variations in Structure from High Resolution Electron Microscope Images by Combining Real Space and Fourier Space Information

“…The bulk lattice parameter of Ni is 14% less than that of Au so we would expect to see variations in the lattice fringe spacings in the image. Similar strained multilayers have been analysed by marking the positions of the peaks in intensity in the image, the separation of the peaks giving the local lattice fringe parameter [18][19][20]. The phase images should provide similar information given the relationship between the gradient of the phase and the local difference in reciprocal lattice fringe vector.…”

“…7). The correct procedure is therefore to obtain a good first estimate of the composition profile from the experimental image, model the layer system taking into account such effects as relaxation [19], and compare the simulations with the experimental data, refining the model as necessary [20].…”