Fabrication of semiconductor nanostructures such as quantum dots
(QDs), quantum rings (QRs) has been considered as the important step for realization
of solid state quantum information devices, including QDs single photon emission
source, QRs single electron memory unit, etc. To fabricate GaAs quantum rings, we
use Molecular Beam Epitaxy (MBE) droplet technique in this report. In this droplet
technique, Gallium (Ga) molecular beams are supplied initially without Arsenic (As)
ambience, forming droplet-like nano-clusters of Ga atoms on the substrate, then the
Arsenic beams are supplied to crystallize the Ga droplets into GaAs crystals. Because
the morphologies and dimensions of the GaAs crystal are governed by the interplay
between the surface migration of Ga and As adatoms and their crystallization, the
shape of the GaAs crystals can be modified into rings, and the size and density can be
controlled by varying the growth temperatures and As/Ga flux beam equivalent
pressures(BEPs). It has been shown by Atomic force microscope (AFM)
measurements that GaAs single rings, concentric double rings and coupled double
rings are grown successfully at typical growth temperatures of 200°C to 300°C under
As flux (BEP) of about 1.0×10-6 Torr. The diameter of GaAs rings is about 30-50 nm
and thickness several nm.