Synthesis and functionalization of epitaxial quantum dot nanostructures for nanoelectronic architectures

We describe methods for assembly of quantum dots (QDs) into arrays of any symmetry, and methods for nanoscale doping of individual QDs. We have previously shown how the Ga⁺ focused ion beam (FIB) can template Si(1 0 0) surfaces for controlled Ge QD nucleation. Local Ga-induced reduction of the wetting layer thickness also suppresses QD nucleation away from the templating sites. This allows synthesis of arrays of any defined geometry and set of spatial frequencies, with positional control of each QD element to ca. 10 nm. We have also applied these methods to "quantum dot molecule" (QDM) structures, that comprise four QDs surrounding a central surface pit and that form spontaneously under conditions of limited adatom mobility in GeSi/Si(1 0 0). Again, the positions and spacings of the QDMs can be controlled by local FIB templating. This creates hierarchical order over multiple lengths scales, from ultra-small dimensions inaccessible to conventional lithography (i.e. nm for QD spacing to tens of nm for individual QD sizes), to much greater length scales (hundreds of μm) over which controlled arrays of QDMs can be fabricated. The ability to bring individual QDs in the QDM into very close proximity (of order nm) has potential applications to nanoelectronic architectures based on electron/hole tunneling or spin interactions. We are developing methods for electronic and magnetic functionalization of these nanostructures using a mass-selected FIB, where ions of different species can be separated from liquid metal alloy sources (e.g. Si from AuSi, B and As from PdAsB, and Mn and Ge from MnGe).