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

The overgrowth of prepatterned GaAs substrates by molecular beam epitaxy (M BE) of GaAs/AlGaAs heterostructures is investigated by scanning electron mi croscopy (SEM) and atomic force microscopy (AFM). First, mesas with vertica l side walls which have a constriction of 1-5 mu m, are patterned into a Ga As substrate. During the MBE deposition of GaAs/AlGaAs layers onto this sub strate, specific facets form at the boundaries of the patterned area. These facets depend on the shape and orientation of the prepatterning. A detaile d study of an overgrown constriction which consists mainly of {110} and int ermediate {N11}A (N = 3 or 4) facets shows that the constriction narrows an d that a rectangular shape of the prepatterning is maintained in the MBE pr ocess. Inter facet diffusion of adatoms modifies the thickness of the MBE l ayers in the patterned area. The enhanced thickness of layers in the center of the constriction may be utilized to fabricate dot and wire like structu res at well-defined positions. AFM measurements in combination with simulat ions of the surface diffusion clearly demonstrate that the {110} facets yie ld the main contribution to the enhanced thickness. {N11}A facets can only be employed to obtain the above enhancements, if the prepatterned constrict ion is round-shaped. This sets a limit for down-scaling to the submicron ra nge. (C) 2000 Elsevier Science S.A. All rights reserved.