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Evolution of strain and composition during growth and capping of Ge quantum dots with different morphologies

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A Bernardi, M I Alonso, J S Reparaz, A R Goñi, P D Lacharmoise, J O Ossó1 and M Garriga

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We follow the growth of islands with different shapes by monitoring the strain relaxation by reflection high energy electron diffraction (RHEED). Comparing a bimodal ensemble of pyramids and domes with a monomodal distribution of C-induced domes, we observe different relaxation pathways and a growth mode change from Stranski–Krastanow to Volmer–Weber. We also study the changes induced by the capping process with Si. Small strains in thin cap layers are revealed by spectroscopic ellipsometry. Raman spectroscopy is employed to probe the built-in strain and silicon intermixing in different types of islands, evidencing that smaller islands are enriched in Si and effectively recompressed, whereas bigger relaxed dots remain substantially unaffected.


PACS

68.65.Hb Quantum dots (patterned in quantum wells)

62.20.D- Elasticity

78.30.Am Elemental semiconductors and insulators

78.67.Hc Quantum dots

62.20.F- Deformation and plasticity

62.25.-g Mechanical properties of nanoscale systems

Subjects

Condensed matter: electrical, magnetic and optical

Semiconductors

Surfaces, interfaces and thin films

Condensed matter: structural, mechanical & thermal

Nanoscale science and low-D systems

Dates

Issue 47 (28 November 2007)

Received 13 July 2007, in final form 26 September 2007

Published 17 October 2007



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