Atomic structure of quantum dots and their bounding facets

Karl Jacobi*, Juan Márquez and Lutz Geelhaar

Fritz-Haber-Institut der Max-Planck-Gesellschaft

Faradayweg 4-6, D-14195 Berlin, Germany

* Tel. xx49-30-8413-5201, Fax. xx49-30-8413-5106, e-mail: jacobi@fhi-berlin.mpg.de

 

InAs was grown by molecular beam epitaxy (MBE) on GaAs(001) until self-assembled three-dimensional islands were formed. At this point the growth was interrupted and the sample was quenched rapidly to room temperature. The shape of the islands, which had the same dimensions known for self-assembled InAs quantum dots, was investigated in situ by ultra-high vacuum scanning tunneling microscopy (UHV-STM). Atomically resolved STM images revealed that the dominating bounding facets of the islands were of high Miller-indices, instead of low ones (i.e., {110}, {111} or {100}).

Although there were some observations of such uncommon bounding facets in the literature, until now it was not possible to determine the exact orientations. At this point our more general efforts to investigate the stability of high-index GaAs surfaces [1-6] helped a lot. Whereas GaAs(112) surfaces decompose into facets [1], (113)A [2], (-1-1-3)B [3] and (114)A [4] turned out to be stable. Even more interesting, a completely new stable surface was discovered within the stereographic triangle, namely (2 5 11) [5,6].

With the help of a comparative STM study on planar (2 5 11)-oriented wafers we have been able to assign unambiguously the main facets of the InAs islands to be of {137} orientation [7], which is only 2.3 off from (2 5 11). Moreover, the experiments on the GaAs(2 5 11) surface indicated that the (137) surface should be energetically unfavorable. As a result, it appears that the dot formation is more complex than suggested by the classical Stranski-Krastanov growth mode.

[1] K. Jacobi, J. Platen, C. Setzer, J. Márquez, L. Geelhaar, C. Meyne, W.Richter, A. Kley, P. Ruggerone, and M. Scheffler, Surf. Sci. 439 (1999)59.

[2] L. Geelhaar, J. Márquez and K. Jacobi, Phys. Rev. B 60 (1999) 15890 and refs.therein.

[3] L. Geelhaar, J. Márquez and K. Jacobi, Phys. Rev. B 62 (2000) 6908.

[4] J. Márquez, P. Kratzer, L. Geelhaar, K. Jacobi and M.Scheffler, PRL 86 (2001) 115.

[5] J. Márquez, L. Geelhaar, and K. Jacobi, Phys. Rev. B 62 (2000) 9969.

[6] L. Geelhaar, J. Márquez, P. Kratzer and K. Jacobi, "GaAs(2 5 11) A new stable surface inside the stereographic triangle", PRL, submitted.

[7] J. Márquez, L. Geelhaar and K. Jacobi, " Atomically resolved structure of InAs quantum dots", Appl. Phys. Lett., submitted.