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Published November 15, 2002 | Published
Book Section - Chapter Open

Structural Transformations in self-assembled Semiconductor Quantum Dots as inferred by Transmission Electron Microscopy


Transmission electron microscopy studies in both the scanning and parallel illumination mode on samples of two generic types of self-assembled semiconductor quantum dots are reported. III-V and II-VI quantum dots as grown in the Stranski-Krastanow mode are typically alloyed and compressively strained to a few %, possess a more or less random distribution of the cations and/or anions over their respective sublattices, and have a spatially non-uniform chemical composition distribution. Sn quantum dots in Si as grown by temperature and growth rate modulated molecular beam epitaxy by means of two mechanisms possess the diamond structure and are compressively strained to the order of magnitude 10 %. These lattice mismatch strains are believed to trigger atomic rearrangements inside quantum dots of both generic types when they are stored at room temperature over time periods of a few years. The atomic rearrangements seem to result in long-range atomic order, phase separation, or phase transformations. While the results suggest that some semiconductor quantum dots may be structurally unstable and that devices based on them may fail over time, triggering and controlling structural transformations in self-assembled semiconductor quantum dots may also offer an opportunity of creating atomic arrangements that nature does not otherwise provide.

Additional Information

© 2002 Society of Photo-Optical Instrumentation Engineers (SPIE). Prior collaborations with G. Roger Booker, Robin J. Nicholas, (both University of Oxford) and Nigel J. Mason (Kamelian Ltd. Oxford) as well as the supply of samples by Jacek K. Furdyna, and Malgorzata Dobrowolska (both University of Notre Dame) are kindly acknowledged. Alan Nicholls (Electron Microscopy Service, University of Illinois at Chicago) is thanked for experimental support. This research was sponsored by both a grant to NDB by the National Science Foundation (DMR-9733895) and a grant to PM by the Campus Research Board of the University of Illinois at Chicago.

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