Nanostructured Poly-Si and Poly-SiGe Layers for Enhanced Energy Harvesting Applications
Résumé
This work investigates a method to fabricate nanostructured polycrystalline Si (poly-
Si) and polycrystalline SiGe (poly-SiGe) layers with high optical absorption and
energy harvesting capabilities. As-grown layers are processed on a glass substrate
using plasma enhanced chemical vapor deposition (PECVD) with a maximum
substrate temperature of 210 . At such a low thermal budget, the deposited layers
are in amorphous form with high sheet resistivity values. A post-processing laser
annealing treatment of these layers is then used to induce surface nano-structuring
and improve their electrical and optical behavior.
The laser’s short pulse duration, 24 ns, and wavelength, 248 nm, imply that most of
the laser energy density is absorbed by the surface of the a-Si and a-SiGe layers,
transforming them to a polycrystalline form upon re-solidification. This guarantees
that the underlying substrate remains at a low thermal point throughout the
fabrication process. As the substrate remains at a reduced temperature, the intention
is that after development of the deposition process and the layer treatment, the
resulting nanostructured layers can be implemented on flexible polymer or other
temperature sensitive substrates.
The optical properties of the fabricated nanostructured layers are analyzed and
variations in the laser energy density, number of pulses and treated material are
compared. We report absorbance enhancement factors in the range of 20 to 25 for
nanostructured poly-Si and as high as 60 for nanostructured poly-SiGe in
comparison to the as-grown layers. As SiGe exhibits thermoelectric behavior, further
studies in this work involve investigating the thermoelectric performance of the
nanostructured poly-SiGe layer. We observe an improvement of 34.4% to the
Seebeck coefficient at a temperature nine times lower than that of other processing
methods reported in literature, such as nano-structuring using mechanical alloying
and thermal annealing approaches.
This work presents a waste free, low thermal budget fabrication method of
nanostructured poly-Si and poly-SiGe layers. We show that a laser nano-structuring
fabrication technique is ideal for applications on temperature sensitive substrates
and enables an integration flexibility with other processing methods. Both
nanostructured poly-Si and poly-SiGe layers exhibit superior optical absorption that
can be fine-tuned depending on the applied laser treatment. An advantage of the
nanostructured poly-SiGe layer, in particular, is its improved thermoelectric
performance, making it a suitable material for hybrid energy harvesting applications.
Domaines
Physique [physics]Origine | Fichiers produits par l'(les) auteur(s) |
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