Biomedical Engineering Reference
In-Depth Information
these results demonstrate the high potential of the droplet epitaxy “nanodrilling”
technique to obtain high optical quality QDMs showing quantum mechanical
coupling signatures in a lateral geometry.
1.3
Fabrication of Lateral Molecular Arrangements of QDs
by Ex Situ Local Oxidation Nanolithography
In this section, we will demonstrate the suitability of ex situ AFM-LAO technique
in combination with MBE growth technique to fabricate site-controlled single InAs
QDs and lateral QDMs-like arrangements on GaAs (0 0 1) substrates. Similarly to
the fabrication process presented in the previous section, this approach is based on
the fabrication of patterned nanoholes that will act as preferential nucleation sites
for QDs formation. Particularly, we will show that by controlling the size/shape of
the patterned nanoholes and the MBE growth conditions of the subsequent epitaxial
deposition, not only the number of QDs in a lateral molecular arrangement can be
controlled but also their position on the substrate, which is also very interesting for
their optimal integration in real and practical devices.
1.3.1
Fabrication of Patterned GaAs (0 0 1) Substrates
by AFM-LAO
AFM-LAO is a well-known technique used for fabricating oxide structures on
surfaces of a wide range of materials under ambient conditions [
56
,
57
]. The AFM-
induced oxidation mechanism is relatively fast (a few milliseconds) and spatially
limited down to nanometric areas with high resolution in the lateral positioning and
size/shape of the oxide structures on the substrate surface. The oxidation mechanism
is a process induced by the application of an external voltage between the AFM
tip and the substrate surface [in this case GaAs (0 0 1)], as sketched in Fig.
1.12
.
Fig. 1.12
Schematic
representation of the
AFM-LAO process. Oxides
structures are formed on
GaAs (0 0 1) substrates as a
consequence of the
reduction/oxidation processes
through a water bridge
