Chemistry Journal Vol. 1, No. 2, 2015, pp. 10-14 http://www.publicscienceframework.org/journal/cj * Corresponding author E-mail address:[email protected] (R. B. Zaghouani) Silver Nanoparticles Effect on Silicon Nanowires Properties R. Benabderrahmane Zaghouani * , S. Aouida, N. Bachtouli, B. Bessais Photovoltaic Laboratory, Research and Technology Centre of Energy, BorjCedria Science and Technology Park, Hammam-Lif, Tunisia Abstract Thiswork focuses on optical characterization of silicon nanowires (SiNWs) used for photovoltaic applications. We report on the elaboration of silicon nanowires by Metal Assisted Chemical Etching (MACE) technique using silver (Ag) as metal catalyst. The obtained resultsshow that the SiNWsoptical properties are sensitive to their elaboration conditions specially the cleaning protocol. The reflectivity was found to be dependent on wavelength and increased from ultra-violet to red wavelength for all tested samples. The comparison between samples with different cleaning protocol shows that, in the UV spectral region, SiNWsmore contaminated with Ag nanoparticles present a pronounced decrease of the reflectivity. This optical behavior was attributed to metallic nanoparticles persisting in the silicon nanowires structures presenting surface plasmon resonance energy in a vicinity of UV spectral region. Keywords SiNWs, MACE, Reflectivity, Silver Nanoparticles, Surface Plasmon Resonance Received: March 5, 2015 / Accepted: March 20, 2015 / Published online: March 24, 2015 @ 2015 The Authors. Published by American Institute of Science. This Open Access article is under the CC BY-NC license. http://creativecommons.org/licenses/by-nc/4.0/ 1. Introduction Silicon-based solar cells remain the main candidate in photovoltaic solar energy conversion [1]. However, a large part of the solar cell conversion-efficiency limits are attributed to the optical losses in silicon material. That’s why the scientific community isinterested in developing concepts and technologies that enable reducing optical losses and thus enhance the solar cell efficiency [2-4]. Conventionally, the surface reflectivity of silicon-based solar cells can be reduced by texturing the front side of the cell [5-7]and/or using appropriate antireflection (AR) coatings[8,9]. During the last decade, important efforts have been dedicated to the use of silicon nanowires structures (SiNWs) in photovoltaic applications. SiNWs deposited on the surface of silicon- based solar cells could act as an efficient antireflection layer. Such structures present highly light absorption behavior which could attain 97% in UV-visible spectral regionsattributed to light confinement of incident light in the nanowires structures, as for porous silicon. Nowadays, silicon nanowires have been integrated in many otherdevices and applications such as silicon nanowire field-effect transistor (SiNW-FET) in microelectronics applications and biological sensorsthanks to their high internal surface [10,11].Many techniques are proposed in order to elaborate homogenous silicon nanowires: bottom up and top down approaches. One of the mostly used methods in the bottom up approaches the vapor Liquid Solid (VLS) method which needs the use of hard equipments like the CVD or PECVD. In this work, we have elaborated silicon nanowires with a top down method: the Metal Assisted Chemical Etching (MACE). This method is simple and can lead to homogenous silicon nanowires. Gold and silver are the most used metals as catalysts. Gold is known to diffuse and create deep-level defects in the silicon band gap [12]. These defects act as recombination centersdeteriorating the electrical properties of
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we have investigated the sensitivity of SiNWs optical
response with the cleaning protocol. In Fig.5(b), we compare
the total reflectivity of SiNWs cleaned in a concentrated
HNO3 solution during 1min (sample A) andSiNWs cleaned in
dilutedsolution (<HNO3:H2O>=<1:1>) during 1 min (sample
B).Sample B, suspected to be more contaminated with Ag-
Nps, exhibits a pronounced decrease of the reflectivity in the
UV spectral regioncomparedto sample A. Fig.6 shows cross-
section SEM images of sample A (Fig.6(a)) and sample B
(Fig.6(b)). We observe that sample B presents effectively a
higher density of Ag-Nps than sample A.These results
support the hypothesis of metallic nanoparticles contribution
on SiNWs optical response.
a
13 R. Benabderrahmane Zaghouani et al.: SilverNanoparticlesEffect on SiliconNanowiresProperties
b
Fig. 5. (a) Reflectivity spectra of SiNWsand bare silicon substrate (b):
Reflectivity spectra of SiNWs: sample A and sample B rinsed in
concentrated and diluted HNO3, respectively.
a
b
Fig. 6. (a) SEM cross-section view of sample A (b): SEM cross-section view
of sample B.
To confirm thisbehavior, we studied the reflectivity of the
dendritic structures. Fig.7 shows the surface reflectivity of
three dendritic layers presenting different densities
(D1>D2>D3).We notice that the curves shape is similar to
those obtained for SiNWs structures. The reflectivity of
different layers is a wavelength-dependant decreasing from
visible to ultraviolet wavelengths. It exhibitsa sharp drop
around 350 nm reaching a minimum in the UV region. The
drop observed is related to the optical response of Ag-Nps in
the UV spectral region attributed to the plasmonic effect.
This optical response presents an evidence of silver
nanoparticles contribution in SiNWs reflectivity.
4. Conclusions
In this work, we have presented the elaboration of silicon
nanowires structuresthat could be integrated in silicon-based
solar cells as antireflection layer. SiNWs are formed by
chemical etching technique assisted by silver. We reported a
detailed study on the effect of silver nanoparticles on the
optical response of silicon nanowires. These nanoparticles
are persisting in the structure even after cleaning with
HNO3and are influencing the SiNWs reflectivity. They
present a plasmonic effect when excited by light leading to a
reflectivity decrease. This property of Ag-Nps seems to be
interesting in order to verify the efficiency of the cleaning
protocol.
Fig. 7. Total reflectivity of three dendritic layers presenting different
densities D1>D2>D3.
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