Self assembling quantum dots (QDs) has been attracted much attention to
formstructures with dimensions on the order of a few
tensof nm that
are necessary for the realization of advanced quantum devices such as quantum
cellular automata (QCA) or the quantum computer. To realize these structures, it is necessary to
control the location of QDs.
In 1990, we have proposed a novel self-assembling growth method, termed Droplet Epitaxy, for the direct formation ofQDs with homogeneous size[1]. We believe this was the first paper
aiming the direct formation ofQDs
without using any lithography. The Stranski-Krastanow type growth, which is used by many
researchers to fabricate QDs, occurs only in the strained systems such as
InGaAs/GaAs. Compared with the island formation based on the Stranski-Krastanow growth mode, the Droplet Epitaxy is applicable to the formation of quantum dots not only in lattice-mismatched but also in lattice-matched systems such as GaAs/AlGaAs. The process of the Droplet Epitaxy in MBE chamber consists of
forming numerous III-column element droplets such as Ga or InGa with
homogeneous size of around 10 nm on the substrate surface first by supplying
their molecular beams, and then reacting the droplets with As molecular beam to
produce GaAs or InGaAs epitaxial microcrystals.
However, whenQDs are formed on a planar substrate by using Droplet Epitaxy, they are randomly distributed in
the location on the substrate. In this presentation, we report
on our recent progress toward the fabrication of site-controlled III-V compound semiconductor QDs by using Droplet Epitaxxy and the lithography based on the Atomic Force Microscopy(AFM).
