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InAs sub-monolayer quantum dots
Sub-monolayer quantum dots are grown by alternating deposition of sub-monolayers of InAs and a few monolayers of GaAs. In this way, a strain-induced stacking of monolayer-high InAs patches is intended, which interact electronically and form zero-dimensional nanostructures. In contrast to Stranski-Krastanow quantum dots, these structures have no wetting layer, being interesting for high-speed optoelectronic applications.
Here the atomic structure of such nanostructures grown by MOCVD was studied using XSTM . It was found that rather small structures with a very high density in the 1012/cm2 range are formed. A strong vertical segregation with segregation lengths around 1 nm is observed. In the case of thin GaAs spacer layers, this leads to vertically coherent InGaAs structures instead of the nominally assumed InAs/GaAs stacks.
(a) XSTM image of 5layers of 0.5 ML InAs separated by 16 layers of GaAs, and (b) variation of the local lattice constant and therewith of the local stoichiometry indicating strong segregation .
 Atomic structure of buried InAs sub-monolayer depositions in GaAs, A. Lenz, H. Eisele, J. Becker, L. Ivanova, E. Lenz, F. Luckert, K. Pötschke, A. Strittmatter, U.W. Pohl, D. Bimberg, and M. Dähne, Applied Physics Express 3, 105602 (2010).