Complete Report - University of New South Wales

PhD student Daniel Inns inspecting EVA poly-
Si thin-fi lm solar cell material fabricated on a
planar sheet of glass.
Silicon Quantum Dots in Silicon Nitride
The same technique previously used to make silicon quantum dots (QDs) by deposition of
thin Si rich layers (4nm) interspersed with thin silicon dielectric layers, used in silicon oxide
based materials, has been successfully applied to silicon nitride based materials. The lower
Si 3 N 4 barrier height should give a higher interdot probability for carrier transport, thus
resulting in a higher conductivity material for the same QD density. The concept will next be
applied to SiC with an even lower barrier height. Transfer to nitride is an important proof of
concept of the transferability of the technology to different material systems. Growth has
been accomplished both by the same reactive sputtering technique used for oxide and with
PECVD. On annealing, both these structures produce nanocrystals of Si limited in size by the
thickness of the Si rich layer – as demonstrated by the TEM images shown. Electron density
contrast for the TEM images of QDs in the nitride is lower than in oxide but the crystal planes
in the Si nanocrystals can still be seen. Characterisation of nanostructures is inherently
diffi cult because of the small sizes involved. Hence in 2005 there has been a signifi cant effort
to improve both the resolution and breadth of nanoscale characterisation techniques. This
has resulted in successful XRD of Si nanostructures which nicely complements TEM data. It
both corroborates the presence of Si nanocrystals and highlights some subtle differences in
lattice parameter which are useful in identifying artifacts in both TEM and XRD.
(a)
120kV TEM image of PECVD deposited (a) Si quantum dots in 10 bi-layers of a silicon-rich-
SiNx /SiNx superlattice and (b) 300kV High Resolution TEM image showing lattice planes in
Si nanocrystals.
(b)
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