Center for Semiconductor Physics in Nanostructures
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Ordered
nano-scale trenches, dots and pillars have been fabricated in and on various
substrates including silicon and gallium arsenide using masks based on
anodic aluminum oxide (AAO) templates formed by electrochemically oxidizing
aluminum. Under the appropriate anodizing conditions, the AAO templates
can form ordered hexagonal arrays of pores with tunable diameters and
pore spacings.
Figure a) shows an example of an AAO template with ordered domains around 1 mm in size. Typical parameters for an ordered porous alumina film formed in an oxalic acid electrolyte are 50 nm pore diameters spaced 100 nm apart. We will report on results obtained using AAO templates directly as masks for a fluorine beam dry etching process as well as an ion beam etching process to fabricate arrays of ordered nano-holes. Using the atomic beam, we have fabricated arrays of 50-70 nm diameter holes in Si and Silicon on Insulator (SOI), while with the ion beam we have etched similar size holes in GaAs.
Figures
b) and c) show examples of these trenches. In the case of SOI, the
oxide layer provides quantization in the depth direction, so that such
silicon nanostructures should show quantum confinement effects.
Using
this technique, we have fabricated arrays of 50 nm diameter dots of various
materials that range anywhere from 10-50 nm in height. These arrays of
dots can themselves be used as masks to create ordered arrays of pillars
via a dry etching process.
Figure
d) shows an example of GaAs pillars on a GaAs substrate fabricated
in this manner using an ion beam etch. We have also used the AAO templates
to deposit arrays of catalyst dots for the growth of carbon nanotubes.
Finally, we will report on several ways to controllably reduce pore diameters
in the AAO templates. In addition, it should be noted that these procedures
can be done remotely in situ in a UHV environment with an MBE system.
--- M.B. Johnson (CSPIN)
