Regensburg 2004 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 3: Quantenpunkte und -dr
ähte: Herstellung und Charakterisierung
HL 3.4: Vortrag
Montag, 8. März 2004, 11:00–11:15, H17
Shape transition during growth of InAs/GaAs quantum dots — •Peter Kratzer1 and Quincy Liu2 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin — 2Hahn-Meitner-Institut, Berlin
Recent STM studies have revealed that free-standing MBE-grown InAs quantum dots on GaAs(001) appear in at least two varieties, as flat structures mainly bounded by (137) facets [1], or also as larger objects with an aspect ratio >0.3, showing a variety of bounding facets [2]. We investigate theoretically the energetics associated with these island shapes, employing a hybrid approach [3]: surface energies and surface stress are calculated using density functional theory, taking into account the specific atomic structure. The bulk elastic energy in both the islands and the substrate is calculated within continuum elasticity theory, using the finite-element method. We find that the flat island shape with (137) facets is energetically preferable for small island volumes, while the steeper shape becomes energetically lower for larger islands. Tensile surface stress and the associated lowering of the surface energy on strained facets plays a decisive role in this cross-over. We discuss implications of our findings for the growth kinetics of InAs islands, in particular for the two-dimensional growth mode of new atomic layers on the strained side facets of the island.
[1] J. Marquez et al., Appl. Phys. Lett. 78, (2001) 2309
[2] G. Costantini et al., Appl. Phys. Lett. 82, (2003) 3194
[3] E. Pehlke et al., Appl. Phys. A 65, (1997) 525