Quantitative study of Cd atoms distribution in CdTe/ZnTe quantum dots superlattice by HRTEM

Slawomir Kret 1Piotr Traczykowski 2Piotr Dłużewski 1Pierre Ruterana 3Paweł Dłużewski 2Marcin Żak 1A. Szczepańska 1S Maćkowski 1Grzegorz Karczewski 1

1. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
2. Polish Academy of Sciences, Institute of Fundamental Technological Research (IPPT PAN), Świętokrzyska 21, Warszawa 00-049, Poland
3. SIFCOM, UMR6176, CNRS-ENSICAEN, 6 Bld Maréchal Juin, Caen 14050, France

Abstract

We investigated the CdTe/ZnTe stacked Quantum Dots (QD) superlattice by High Resolution Transmission Electron Microscopy (HRTEM). In the superlattice with 2 ML thick CdTe layer separated by 15 ML thick ZnTe spacer zones of autocorrelation arrangement of QDs was observed on cross-sectional samples . In the plane-view images of single QDs layer taken in <001> zone axis , it can be noticed that the islands have an asymmetric ellipsoid shape along the [100] and [010] directions, the two axis being 6-7nm and 3-4 nm in magnitude respectively and that their heights are below 1.5 nm. The measured strain ε[001] component suggests the existence of a composition gradient in the lateral as well as in the vertical directions.
Model of super cell containing the cadmium rich QDs with Cd0.8Zn0.2Te 1ML wetting layer was "relaxed" by molecular static elastic energy minimization. We have applied the discrete Stillinger-Weber (S-W) potential to Finite Element (FE) solver. For the purpose we have developed novel mesh generator which produced pseudo-elements compatible with S-W energy equations. The supercell with equilibrium x,y,z position of atoms obtained for boundary conditions corresponding to TEM was used to calculate images.The model verification is performed by the comparison of the strain maps measured from simulated images (Figure 2b) strain maps and experimental ones. Although, our approach cannot give unequivocal 3D distribution of cadium atoms in observed zone but the realistic model of anticorrelated CdTe/ZnTe QDs is possible to be obtained after few additional steps of model optimization.

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Presentation: poster at E-MRS Fall Meeting 2004, Symposium D, by Slawomir Kret
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-08-03 17:03
Revised:   2009-06-08 12:55
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