Águas, H., Martins Fortunato R. E. "
Influence of the plasma regime on the structural, optical and transport properties of a-Si:H thin films."
Key Engineering Materials. 230-232 (2002): 583-586.
AbstractIn this work we show that it is possible to control the plasma species present near the substrate surface, from what is usually associated with an α regime (a plasma free of particles) to a γ' regime (a plasma where particles are present) and simultaneously control the energy of the ions striking the substrate during a-Si:H deposition from a silane glow discharge in a modified triode (MT) type PECVD reactor, where a DC mesh electrode biased with Vpol is located in front of the r.f electrode. The presence of large particles in the plasma leads to the deposition of the films with the poorest optoelectronic properties. When the particle size in the plasma decrease the film properties improve, but, when particles are no longer present in the plasma region close to the substrate, like in a α like regime, the properties of the films deteriorate again. The results show that the best transport properties are achieved for the films deposited in the α-γ' transition regime corresponding to 0V<Vpol<51V. Under this condition the films present a dark conductivity, σ d ≈ 10-11 (Ωcm)-1, photosensitivity, S ≈ 107, activation energy, ΔE ≈ 0.9 eV, hydrogen content, CH ≈ 10%, factor of microstructure, R ≈ 0.085 and an optical gap, Eop ≈ 1.77 eV.
b c Nedev, N.a b, Beshkov Fortunato Georgiev Ivanov Raniero Zhang Martins G. a E. b. "
Influence of the rapid thermal annealing on the properties of thin a-Si films."
Materials Science Forum. 455-456 (2004): 108-111.
AbstractThe variation of the structure, morphology and the electrical properties of thin amorphous silicon films caused by Rapid Thermal Annealing is studied. The films annealed at 1200°C for 2 minutes change their structure to polycrystalline and as a result their resistivity decreases by 4 orders of magnitude. Due to the small thickness of the as deposited amorphous silicon the obtained poly-Si is strongly irregular and has many discontinuities in its texture.
Araújo, A., Mendes Mateus Vicente Nunes Calmeiro Fortunato Águas Martins M. J. T. "
Influence of the Substrate on the Morphology of Self-Assembled Silver Nanoparticles by Rapid Thermal Annealing."
Journal of Physical Chemistry C. 120 (2016): 18235-18242.
AbstractMetal nanoparticles are of great interest for light trapping in photovoltaics. They are usually incorporated in the rear electrode of solar cells, providing strong light scattering at their surface plasmon resonances. In most cases, the nanoparticles are self-assembled by solid-state dewetting over a transparent conductive oxide (TCO) layer incorporated in the cell's rear electrode. Up to now, this process has been optimized mainly by tuning the thermal annealing parameters responsible for dewetting, or the thickness of the precursor metallic layer; but little attention has been paid to the influence of the underlying TCO layer properties on the morphology of the nanoparticles formed, which is the focus of the present article. This work investigates Ag nanoparticles structures produced on distinct surfaces by a simple, fast and highly reproducible method employing rapid thermal annealing. The results indicate that both the thermal conductivity and surface roughness of the TCO layer play a determinant role on the morphology of the nanostructures formed. This is of particular relevance, since we show in the study performed that the parasitic absorption of these Ag nanostructures is reduced, while the scattering is enhanced when the Ag nanostructures are formed on TCO layers with the highest conductivity and the lowest surface roughness (∼1 nm). These results unveil novel possibilities for the improvement of plasmonic nanostructures fabricated by thermal dewetting, via the careful adjustment of the physical properties of the underlying surface. © 2016 American Chemical Society.