The formation of GaSb nanostructures grown by MBE and MOCVD on GaAs(001) was studied using XSTM and XSTS. The GaSb/GaAs system is of particular interest because of the type-II band offset, allowing large hole localization energies in GaSb nanostructures with possible applications as nanoscale memories.
In contrast to the InAs quantum dot system, here mostly GaSb ring structures are observed, which are filled by almost pure GaAs, and the wetting layer is strongly intermixed and partly interrupted [1,2]. Only in the case of very small nanostructures compact dot structures are formed [3]. These effects are related to strong segregation processes mainly during capping. Furthermore, spectroscopy studies revealed the type-II band offset [4].

(a) XSTM image of GaSb quantum rings and (b) sketch of the different cleavage positions [1,2].

Detailed XSTM image of a GaSb quantum ring [1,2].

(a) XSTM image of a GaSb quantum ring with indicated positions of (b) local XSTS spectra demonstrating the type-II band offset. 



[1] Self-organized formation of GaSb/GaAs quantum rings, R. Timm, H. Eisele, A. Lenz, L. Ivanova, G. Balakrishnan, D.L. Huffaker, and M. Dähne, Physical Review Letters 101, 256101 (2008).
[2] Quantum ring formation and antimony segregation in GaSb/GaAs nanostructures, R. Timm, A. Lenz, H. Eisele, L. Ivanova, M. Dähne, G. Balakrishnan, D.L. Huffaker, I. Farrer, and D.A. Ritchie, Journal of Vacuum Science and Technology B 26, 1492 (2008).
[3] Structure and intermixing of GaSb/GaAs quantum dots, R. Timm, H. Eisele, A. Lenz, S.K. Becker, J. Grabowski, T.-Y. Kim, L. Müller-Kirsch, K. Pötschke, U.W. Pohl, D. Bimberg, and M. Dähne, Applied Physics Letters 85, 5890 (2004).
[4] Confined states of individual type-II GaSb/GaAs quantum rings studied by cross-sectional scanning tunneling spectroscopy, R. Timm, H. Eisele, A. Lenz, L. Ivanova, V. Vossebürger, T. Warming, D. Bimberg, I. Farrer, D.A. Ritchie, and M. Dähne, Nano Letters 10, 3972 (2010).