  This paper has been withdrawn by the authors. The 3D distribution of
self-assembled stacked quantum dots (QDs) is a key parameter to obtain the
highest performance in a variety of optoelectronic devices. In this work, we
have measured this distribution in 3D using a combined procedure of
needle-shape specimen preparation and electron tomography. We show that
conventional 2D measurements of the distribution of QDs are not reliable, and
only a 3D analysis allows an accurate correlation between the growth design and
the structural characteristics.
