SiNx:Tb3+--Yb3+, an efficient down-conversion layer compatible with a silicon solar cell process

SiN x : Tb 3+-Yb 3+, an efficient down-conversion layer compatible with silicon solar cell process Abstract Tb 3+-Yb 3+ co-doped SiN x down-conversion layers compatible with silicon Photovoltaic Technology were prepared by reactive magnetron co-sputtering. Efficient sensitization of Tb 3+ ions through a SiN x host matrix and cooperative energy transfer between Tb 3+ and Yb 3+ ions were evidenced as driving mechanisms of the down-conversion process. In this paper, the film composition and microstructure are investigated alongside their optical properties, with the aim of maximizing the rare earth ions incorporation and emission efficiency. An optimized layer achieving the highest Yb 3+ emission intensity was obtained by reactive magnetron co-sputtering in a nitride rich atmosphere for 1.2 W/cm${}^2$ and 0.15 W/cm${}^2$ power density applied on the Tb and Yb targets, respectively. It was determined that depositing at 200 {\textdegree}C and annealing at 850 {\textdegree}C leads to comparable Yb 3+ emission intensity than depositing at 500 {\textdegree}C and annealing at 600 {\textdegree}C, which is promising for applications toward silicon solar cells.Comment: Solar Energy Materials and Solar Cells, Elsevier, 201

RBS Analysis of Down-conversion Layers Comprising Two Rare-Earth Elements

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Ellipsometry study of CdSe thin films deposited by PLD on ito coated glass substrates

Cadmium selenide (CdSe) thin films were deposited on indium tin oxide (ITO) coated glass substrates using pulsed laser deposition (PLD) technique under different growth temperatures. Samples were investigated for their structural, morphological, and optical properties through X-ray diffraction (XRD), atomic force microscopy (AFM), and UV-Vis-NIR spectroscopy. AFM analysis revealed that the surface roughness of the as-grown CdSe thin films increased with the increase in deposition temperature. The optical constants and film thickness were obtained from spectroscopic ellipsometry analysis and are discussed in detail. The optical band gap of the as-grown CdSe thin films, calculated from the Tauc plot analysis, matched with the ellipsometry measurements, with a band gap of ~1.71 eV for a growth temperature range of 150◦C to 400◦C. The CdSe thin films were found to have a refractive index of ~3.0 and extinction coefficient of ~1.0, making it a suitable candidate for photovoltaics

(Invited) Enhancing the Blue Emission in Ce Doped Silicon Oxynitrides Thin Films for Electroluminescence Device Applications

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(Invited) Naked Eye Blue Emission in Ce 3+ Codoped SiO x N y : Toward Si-Based Light-Emitting Devices

International audienceRare earth (RE) doped silicon host matrices has been broadly investigated to procure light emitting sources for integrated optoelectronics devices using the RE inter-4f transitions. Classically, those transitions are partially allowed and result in a very low absorption cross section inducing a non-efficient excitation. Due to its 5d-4f transitions, Ce 3+ ion is quite different from other RE 3+ ions due to a large absorption cross section (10 -19 cm -2 ) as compared to the other RE 3+ ions (10 -21 cm -2 ). [1] Furthermore, due to its single valence d -orbital electron, the 5 d band is strongly dependent on the local environment, resulting typically in a large Stokes shift depending on the host matrix composition. [2] Ce-doped SiO x N y films have been deposited by magnetron reactive sputtering from Si and CeO 2 targets under nitrogen reactive gas atmosphere, with a typical thickness of 120 nm. Three investigation approaches were explored. In the first one samples grown with nitrogen highly rich plasma and a low Ce concentration (0.3 at.%) were tested. Photoluminescence (PL) experiments show a wide blue emission band ranging from 400 to 650 nm under UV photons excitation. Reference samples grown with lower nitrogen content did not show any visible emission. To explain the blue emission origin, we have studied extensively the role of different RE ions emitting centers in Ce-doped SiO x N y films ( e.g. band tails, CeO 2 , Ce clusters, Ce 3+ ions), with different activation scenarios. The results confirmed that blue emission is mainly due to the Ce 3+ ion. In addition, based on refractive index measurements, the Ce-doped SiO x N y films compositions were deduced from a Bruggeman effective medium model, confirming the presence of Si 3 N 4 and SiO 2 phases. Furthermore, the presence of those phases was confirmed independently by their bonding signatures identified by infrared spectroscopy (FTIR) analysis. By means of photoluminescence excitation spectroscopy (PLE), a wide excitation range from 250 to 400 nm was evidenced and various excitation channels of Ce 3+ ions involving direct or indirect mechanisms were proposed. In the second approach, we focused on samples grown at high nitrogen flow, where the effect of Ce 3+ concentration variation was investigated. Under UV excitation, a strong blue emission is visible to the naked eyes for SiO x N y sample doped with high Ce 3+ concentration (6 at. % as determined by RBS measurements). The external quantum efficiency was measured for the selected best emitting samples with help of integrating sphere. No saturation of the PL intensity was observed, demonstrating the absence of Ce clusters and/or silicate phase formation due do the nitrogen content. [3] We believe that this result is very promising for considering silicon based emitting applications. Finally, in the third approach we measured electroluminescence (EL) from Ce-doped SiO x N y prototype devices. Signal evolution was investigated as the function of the N flow, the Ce concentration and the inclusion of Al dopants with the aim to improve the electrical conductivity. The influence of these factors on observed EL was studied through the conduction mechanisms. [1] J.M. Ramírez, A. Ruiz-Caridad, J. Wojcik, A.M. Gutierrez, S. Estradé, F. Peiró, P. Sanchís, P. Mascher, B. Garrido, "Luminescence properties of Ce3+ and Tb3+ co-doped SiOxNy thin films: Prospects for color tunability in silicon-based hosts", J. Appl. Phys., 119 ( 2016 ) 113108. [2] J. Li, O.H.Y. Zalloum, T. Roschuk, C.L. Heng, J. Wojcik, P. Mascher, "Light Emission from Rare-Earth Doped Silicon Nanostructures", Advances in Optical Technologies, 2008 ( 2008 ) 10. [3] C. Labbé, Y.T. An, G. Zatryb, X. Portier, A. Podhorodecki, P. Marie, C. Frilay, J. Cardin, F. Gourbilleau, "Structural and emission properties of Tb 3+ -doped nitrogen-rich silicon oxynitride films", Nanotech., 28 ( 2017 ) 115710 (115714pp)

A Systematic Study of Plasma Activation of Silicon Surfaces for Self Assembly

We study the plasma activation systematically in an attempt to simplify and optimize the formation of hydrophilic silicon (Si) surface critical for self-assembly of nanostructures that typically uses <i>piranha</i> solution, a high molarity cocktail of sulfuric acid and hydrogen peroxide at elevated temperatures. In the proposed safer and simpler approach, O₂ plasma is used under optimized process conditions in a capacitively coupled parallel-plate chamber to induce strong hydrophilic behavior on silicon surfaces associated with the formation of suboxide groups. Surface activation is validated and studied via contact angle measurements as well as XPS spectra and consequently optimized using a novel atomic force spectroscopy approach, which can streamline characterization. It is found that plasma power around 100 W and exposure duration of ∼65 s are the most effective parameters to enhance surface activation for the reactive ion etcher system used. Other optimum plasma process conditions for pressure and flow-rate are also reported along with temporal development of activation, which peaks within 1 h and wears off in 24 h scale in air. The applicability of the plasma approach to nanoassembly process was demonstrated using simple drop coating and spinning of polystyrene (<i>d</i> < 500 nm, 2.5–4.5% w/v) and inkjet printing on polydimethylsiloxane

Growth and study of Tb3+ doped Nb2O5 thin films by radiofrequency magnetron sputtering: photoluminescence properties

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Synthesis, Characterization and Fabrication of Graphene/Boron Nitride Nanosheets Heterostructure Tunneling Devices

Various types of 2D/2D prototype devices based on graphene (G) and boron nitride nanosheets (BNNS) were fabricated to study the charge tunneling phenomenon pertinent to vertical transistors for digital and high frequency electronics. Specifically, G/BNNS/metal, G/SiO2, and G/BNNS/SiO2 heterostructures were investigated under direct current (DC-bias) conditions at room temperature. Bilayer graphene and BNNS were grown separately and transferred subsequently onto the substrates to fabricate 2D device architectures. High-resolution transmission electron microscopy confirmed the bilayer graphene structure and few layer BNNS sheets having a hexagonal B3-N3 lattice. The current vs voltage I(V) data for the G/BNNS/Metal devices show Schottky barrier characteristics with very low forward voltage drop, Fowler-Nordheim behavior, and 10&minus;4 Ω/sq. sheet resistance. This result is ascribed to the combination of fast electron transport within graphene grains and out-of-plane tunneling in BNNS that circumvents grain boundary resistance. A theoretical model based on electron tunneling is used to qualitatively describe the behavior of the 2D G/BNNS/metal devices