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Strain profiles in pyramidal quantum dots by means of atomistic simulation

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3 Author(s)
Kikuchi, Y. ; Department of Mechanical Engineering and Intelligent Systems, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan ; Sugii, H. ; Shintani, K.

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The minimum energy configurations of the atomic structure of a Ge island on a Si(001) substrate are calculated by using the conjugate gradient minimization of the potential energy of the system. The island is assumed to be covered or uncovered by a Si layer and assumed to be of pyramidal shape with the sidewalls of {110} or {105} facets; the base length of the island ranges from 5.43 to 10.9 nm. Two empirical potentials, the Keating and Stillinger–Weber potentials, are used. At the interfaces between the regions occupied by the atoms of different species, the potential parameters for such bondings are properly adopted. The strain profiles along the three selected paths within the structure and along the cap surface are calculated. While the profiles of the normal strain component Єxx obtained by the two potentials are in good agreement with each other except within the substrate and at the edges of the island in the uncovered structures, the two profiles of the normal strain component Єzz show a considerable difference in their magnitude, and the use of the Stillinger–Weber potential is recommended for the islands of the small sizes below 10 nm. The validity of the valence force field model with the Keating potential for such small islands is questionable although this model is widely recognized to be applicable to the calculation of strains in the quantum dot structures. The strain relaxation in the uncovered island is discussed through the comparison with that in the covered island. The strain profile along the cap surface explains vertical self-organization of stacked dots. © 2001 American Institute of Physics.

Published in:

Journal of Applied Physics  (Volume:89 ,  Issue: 2 )