Structural and optical characterization of pure Si-rich nitride thin films

International audienceThe specific dependence of the Si content on the structural and optical properties of O-and H-free Si-rich nitride (SiN x>1.33) thin films deposited by magnetron sputtering is investigated. A semiempirical relation between the composition and the refractive index was found. In the absence of Si-H, N-H, and Si-O vibration modes in the FTIR spectra, the transverse and longitudinal optical (TO-LO) SiN stretching pair modes could be unambiguously identified using the Berreman effect. With increasing Si content, the LO and the TO bands shifted to lower wavenumbers, and the LO band intensity dropped suggesting that the films became more disordered. Besides, the LO and the TO bands shifted to higher wavenumbers with increasing annealing temperature which may result from the phase separation between Si nanoparticles (Si-np) and the host medium. Indeed, XRD and Raman measurements showed that crystalline Si-np formed upon 1100°C annealing but only for SiN x0.9 , demonstrating that this PL is not originating from confined states in crystalline Si-np. As an additional proof, the PL was quenched while crystalline Si-np could be formed by laser annealing. Besides, the PL cannot be explained neither by defect states in the bandgap nor by tail to tail recombination. The PL properties of SiN x>0.9 could be then due to a size effect of Si-np but having an amorphous phase

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

Thin films based on Silicon nanostructures for third generation solar cells

L'association du concept de troisième génération de cellules solaires et de la technologie de fabrication des films minces ouvre la voie à l'élaboration de matériaux entrant dans le cadre des énergies renouvelables. Les effets de confinement quantiques observés dans les nanostructures de silicium sont exploités pour une intégration dans des dispositifs du type cellule tandem tout-silicium. Cette thèse vise à comprendre la formation de nanoparticules de silicium dans deux types de matrices diélectriques (SiO2 et SiNx) sous forme de mono- et multi-couches. La matrice de nitrure de silicium possède l'avantage de pouvoir intégrer une densité élevée de nanoparticules (1020 Si-np/cm3) qui après recuit rapide (1min-1000C) conduit à une émission intense dans le domaine visible. Une investigation théorique détaillée des mécanismes d'émission et des facteurs influençant la luminescence est mise en regard des résultats expérimentaux. Les simulations indiquent les caractéristiques d'émission (intensité et énergie) dépendent non seulement de la densité et de la taille des nanoparticules de silicium, mais également de la géométrie (épaisseur des couches et sous-couches, nombre de motifs alternés) et des indices dont le rôle crucial doit être pris en compte pour permettre une intégration dans les dispositifs finalisés.The combination of third generation solar cell concepts in second generation thin film materials has been identified as an efficient way to solve the global energy needs. The quantum confinement effects observed from Si nanostructures are promising towards integration in a third generation solar cell such as an All-Si tandem cell . This thesis focuses on understanding the formation of Si quantum dots (i.e Sinanoparticles) in two kinds of dielectric matrix: SiO2 and Silicon nitride, in monolayer and multilayer (ML) configurations. The advantages of SRSO/SRSN ML over SRSO/SiO2 ML are demonstrated. High density of Si-np (about 1020 Si-np/cm3) and intense emission in visible range are obtained in SRSO/SRSN ML after a short annealing time (1min- 1000C), which is promising for device applications at a reduced thermal budget. A detailed investigation on emission mechanisms and factors that influence emission is made experimentally and theoretically. Simulations indicate that the density of Si-np and their size are not the only parameters that influence the emission intensity and peak positions. The demonstrated influence of geometrical and optical effects on emission is very important towards proceeding with the next step of device integrations.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Characterization and Metrology of Nanoclusters-Based Nanostructures

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Enhancing The Optical And Electrical Properties of Si-based Nanostructured Materials

International audienceMultilayer structures of Si rich silicon oxide (SiOx) alternated with two types of dielectric sublayers viz. SiO2 or SiNx have been studied. An enhancement in the density of nanoclusters within the SiOx sublayer is achieved by using the reactive magnetron co-sputtering method. The effect of SiNx sublayer thickness on the photoluminescence properties is investigated. We succeed in enhancing the absorption and the pholuminescence properties of the multilayers by replacing SiO2 by SiNx sublayers. We also achieve a higher conductivity in SiOx/SiNx with an improved thermal budget. This preliminary study gives a deep insight to optimize materials for future solar cell device applications with enhanced properties at reduced thermal budget

Silicon Nanostructures for Photovoltaics

International audienceSiOx/SiO2 and SiOx/SiNx multilayers have been grown by reactive magnetron sputtering. Different fabrication parameters have been studied to optimize the density of Si nanoparticles (Si-nps) within the SiOx sublayer. The aim is to favor the optical properties of the film as well as the carrier transport for the future development of Si-np-based solar device. This chapter evidences the beneficial role of the SiNx sublayer on the achievement of good optical properties in a lower thermal budget with respect to the SiOx/SiO2 counterparts