Manipulation of the aspect ratio by appropiate exposure design. Comparison of the aspect ratio before and after the buffer layer growth. Two dots with a certain distance are exposed to the resist (a) in order to define an elongated structure, see (b). The attachment of GaAs depends strongly on the crystallographic direction leading to an elongated structure perpendicular to the previous one, see (c). This elongation leads to a nucleation of QDs along a chain, see (d), and is therefore undesired. With increasing distance of the two exposure spots, it is shown in (e) to increase the aspect ratio before the buffer layer growth and therefore decrease the aspect ratio after the buffer layer growth due to the different migration rates.
Mayer et al. Nanoscale Research Letters 2013 8:504 doi:10.1186/1556-276X-8-504