Undoped and Nd3+ doped Si-based single layers and superlattices for photonic applications

International audienceThis work presents the benefits of the superlattice approach to control light emission properties of materials with Si nanoclusters and rare‐earth ions. The undoped and Nd3+‐doped both Si‐rich‐SiO2 single layers and Si‐rich‐SiO2/SiO2 superlattices were grown by radio frequency magnetron sputtering. Their properties were investigated by means of spectroscopic ellipsometry, Fourier infrared transmission spectroscopy, transmission electron microscopy, and photoluminescence (PL) methods versus deposition conditions, annealing treatment, and superlattice design (doping and thickness of alternated sublayers). An intense Nd3+ emission from as‐deposited single layers and superlattices was observed. The lower annealing temperature (below 900 °C) of the single layers and superlattices favors the formation of amorphous Si clusters that act as effective sensitizers of rare‐earth ions. The highest Nd3+ PL intensity was achieved after a conventional annealing at about 600–800 °C in nitrogen flow for all samples. Crystallized Si‐nanoclusters were formed in Si‐rich‐SiO2 single layers upon annealing at 1000–1100 °C, whereas their formation in the superlattices occurred at higher temperatures (1100–1150 °C). The mechanism of Nd ions' excitation via energy transfer from Si‐nanoclusters and/or matrix defects, if any, is discussed

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

Effect of annealing treatments on photoluminescence and charge storage mechanism in silicon-rich SiNx:H films

In this study, a wide range of a-SiNx:H films with an excess of silicon (20 to 50%) were prepared with an electron-cyclotron resonance plasma-enhanced chemical vapor deposition system under the flows of NH3 and SiH4. The silicon-rich a-SiNx:H films (SRSN) were sandwiched between a bottom thermal SiO2 and a top Si3N4 layer, and subsequently annealed within the temperature range of 500-1100°C in N2 to study the effect of annealing temperature on light-emitting and charge storage properties. A strong visible photoluminescence (PL) at room temperature has been observed for the as-deposited SRSN films as well as for films annealed up to 1100°C. The possible origins of the PL are briefly discussed. The authors have succeeded in the formation of amorphous Si quantum dots with an average size of about 3 to 3.6 nm by varying excess amount of Si and annealing temperature. Electrical properties have been investigated on Al/Si3N4/SRSN/SiO2/Si structures by capacitance-voltage and conductance-voltage analysis techniques. A significant memory window of 4.45 V was obtained at a low operating voltage of ± 8 V for the sample containing 25% excess silicon and annealed at 1000°C, indicating its utility in low-power memory devices

SiOx/SiNy multilayers for photovoltaic and photonic applications

Microstructural, electrical, and optical properties of undoped and Nd3+-doped SiOx/SiNy multilayers fabricated by reactive radio frequency magnetron co-sputtering have been investigated with regard to thermal treatment. This letter demonstrates the advantages of using SiNy as the alternating sublayer instead of SiO2. A high density of silicon nanoclusters of the order 1019 nc/cm3 is achieved in the SiOx sublayers. Enhanced conductivity, emission, and absorption are attained at low thermal budget, which are promising for photovoltaic applications. Furthermore, the enhancement of Nd3+ emission in these multilayers in comparison with the SiOx/SiO2 counterparts offers promising future photonic applications

Manipulation de nanoparticules de Si elaborées par implantation ionique à basse énergie dans des couches minces de SiO2 pour la fabrication de mémoires MOS non volatiles

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Élaboration et caractérisation de nanoparticules de silicium dans du nitrure de silicium en vue d applications photovoltaïques

Les nanoparticules de silicium (Si-nps) enfouies dans une matrice de nitrure de silicium (SiNx) sont prometteuses pour les applications photovoltaïques. Cette thèse traite de leur élaboration et leur caractérisation dans le SiNx afin de maitriser leurs propriétés optiques par l intermédiaire du confinement quantique. Des couches minces ( 100nm) SiNx riche en silicium (NSRS) sont préalablement déposées par PECVD. Elles sont ensuite recuites à 1100C/30min pour permettre la nucléation des Si-nps dans la matrice de nitrure de silicium. Nous montrons que le contrôle de l excès de Si permet d engendrer une grande diversité de nanostructures (forte densité -2x1012 cm-2- de Si-nps amorphes de 3 nm de taille moyenne, nanostructures percolées de silicium cristallin, arrangements nano-colonnaires cristallins). Cependant la large distribution de tailles de Si-nps générée par cette approche limite le contrôle efficace des propriétés optiques. Pour cela, nous avons élaboré et caractérisé des super-réseaux composés alternativement de couches NSRS et SiO2 ou Si3N4. Ces dernières permettent de limiter la croissance des Si-nps au moins dans une direction et ainsi d affiner la distribution de tailles des Si-nps. Nous avons déterminé les conditions d élaboration optimales de ces super-réseaux permettant d obtenir des Si-nps de tailles contrôlées compatibles avec le confinement quantique (<5nm). Finalement, des mesures de résistivité des couches NSRS ont été réalisées afin d apprécier les problèmes de transport de charges électriques dans les systèmes Si-nps/SiNx en vue de leur intégration dans les cellules photovoltaïques à multi-jonctions.Silicon nanoparticles (Si-nps) embedded in a silicon nitride matrix (SiNx) are promising for photovoltaic applications. These applications require tuning the optical properties of the films by managing the quantum confinement of the Sinps. This thesis work deals with the elaboration and characterization of silicon nanostructures embedded in silicon nitride. Thin films ( 100nm) of silicon rich silicon nitride (SRSN) have been deposited by PECVD and subsequently annealed at 1100C/30min to allow the nucleation of Si-nps. We show that the control of the silicon excess generates a large diversity of nanostructures including a high density (2x1012 cm-2) of amorphous Si-nps with an average size of 3nm, percolated crystalline nanostructures or nano-columnar crystalline arrangements. However, the large size distribution of Si-nps fathered by the single layer approach limits the control of the optical properties expected by quantum confinement in Si-nps. Then, we have investigated the formation and characterization of super-lattices composed of alternative layers of SRSN and SiO2 or Si3N4 ultrathin films. These stoichiometric layers have been used to limit the Si-nps growth in order to thin down the size distribution. We have identified the experimental parameters, namely the Si excess and the thickness of the SRSN, needed for the formation of Si-nps with size small enough to be compatible with quantum confinement. Finally resistivity experiments in the system Si-nps-Si3N4 have been conducted in order to identify the electrical transport problems that should be overcome for coming application as PV tandem cell for instance.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Ultra-low-energy Ion Beam Synthesis for Nanotechnology and Nanostructures

International audienc

Structural analysis of the interface of silicon nanocrystals embedded in a Si3N4 matrix

cited By 3International audienceThe structure and interface states of thin nanocomposite layers containing Si nanocrystals embedded in an amorphous nitride matrix have been analyzed by Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). The Si 2p core-level spectrum of the nanocomposite layer was deconvoluted by using five Gaussian-Lorentzian contributions corresponding to the different nitride states of Si. It was shown that the Si-ncs/Si3N4 interfaces formed during annealing are composed of a high density of Si2+ subnitrides. These subnitrides are more likely to be responsible for the shoulder at 494cm-1 on the Raman spectra. Considering the proportion of Si2+ subnitrides with respect to Si0 states, an abrupt transition from the crystalline to the amorphous phase due to Si 2=N-Si bridge bonds is suggested

Hybrid systems with Ag nanocrystals and Si nanostructures synthesized by ultra-low-energy ion beam synthesis

International audienceHybrid systems based on silicon and silver nanocrystals (Si-NCs and Ag-NCs) are of considerable interest in photon conversion solar cells. Due to their plasmonic properties, Ag-NCs strongly increase the photoluminescence emission intensity of Si-NCs located in their vicinity, allowing, in principle, to solve the problem of their low emission yield. In this work, we have elaborated 2D networks of Ag-NCs and amorphous Si nanoparticles in a controlled way by using Ultra-Low-Energy Ion-Beam-Synthesis. In the proposed synthesis scheme, a 2D layer of Si-NCs is first obtained by implanting Si+ ions at ultra low energy (from 1 to 3 keV) in a SiO2 layer with subsequent high temperature thermal annealing. Then, Ag+ ions are implanted in the same matrix at energies between 3 and 10 keV and crystalline Ag-NCs are formed during the implantation step. Several configurations with either 2D arrays or a large band of Ag-NCs have been obtained following the Ag+ implantation energy. Enhancement of the PL emission from Si nanostructures, which is related to the presence of Ag-NCs, has been observed under specific arrangement of the two embedded subsystems. In this type of synthesis, a combination of physical phenomena including ion mixing, implantation damage, point defect, and thermal diffusion has been taken into account in order to explain and thus control the structural and the optical characteristics of the system