Systematic growth studies of narrow constrictions formed by molecular beam epitaxy on prepatterned substrates

Abstract

The overgrowth of prepatterned GaAs substrates by molecular beam epitaxy (MBE) of GaAs/AlGaAs heterostructures is investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). First, mesas with vertical side walls which have a constriction of 1–5 μm, are patterned into a GaAs substrate. During the MBE deposition of GaAs/AlGaAs layers onto this substrate, specific facets form at the boundaries of the patterned area. These facets depend on the shape and orientation of the prepatterning. A detailed study of an overgrown constriction which consists mainly of {110} and intermediate { N11}A ( N=3 or 4) facets shows that the constriction narrows and that a rectangular shape of the prepatterning is maintained in the MBE process. Inter facet diffusion of adatoms modifies the thickness of the MBE layers in the patterned area. The enhanced thickness of layers in the center of the constriction may be utilized to fabricate dot and wire like structures at well-defined positions. AFM measurements in combination with simulations of the surface diffusion clearly demonstrate that the {110} facets yield the main contribution to the enhanced thickness. { N11}A facets can only be employed to obtain the above enhancement, if the prepatterned constriction is round-shaped. This sets a limit for down-scaling to the submicron range.