78 research outputs found
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
Photoluminescence of Nd-doped SnO2 thin films
Structural, optical, and electrical properties of Nd-doped SnOx thin films are reported. The atomic structure was characterized by x-ray diffraction and infrared absorption spectrometry. Investigation of the photoluminescence properties revealed Nd-related bands at 920 and 1100 nm for samples annealed at 700 degrees C, which present the tetragonal structure of the SnO2 rutile phase. Nd3+ ions can be indirectly excited and no concentration quenching was observed up to 3 at. %. It is concluded that Nd3+ ions are efficient optically active dopants in addition to be responsible of the observed electric conductivity improvement. These materials are then interesting for solar cell applications
Optical and structural properties of Nd doped SnO2 powder fabricated by the sol-gel method
We report on the structural and optical properties of undoped and neodymium doped SnO2 powders (0, 1, 3, and 5 at% of Nd) synthesized by the sol-gel method. SEM and TEM microscopy techniques reveal a nanometric scale of the powders. We show that the tetragonal rutile phase is achieved after annealing at 700 degrees C. The crystallite size of the doped SnO2 is found to decrease gradually with the increase of Nd content without changing the SnO2 structure. A strong decrease in the intensity of the Raman peaks is noted for doped powders, which can be attributed to the location of Nd3+ ions at the Sn sites indicating Nd incorporation into the host matrix. For the first time the optical properties were studied by UV-VisNIR spectroscopy and revealed Nd related absorption bands in the SnO2 matrix. The investigation of the photoluminescence properties shows broad emission centred around 550-650 nm originating from defects present in the SnO2 host matrix. Under 325 nm laser excitation, a strong photoluminescence of trivalent Nd is observed in the infrared region and shows Nd related emission peaks at 885, 1065, and 1336 nm. Such a strong PL signal under laser excitation indicates that Nd3+ is optically active. The excitation dependent PL (PLE) recorded in the 450-700 nm range confirms the presence of active Nd3+ successfully inserted into the SnO2 host matrix
Structural, optical, and electrical properties of Yb-doped ZnO thin films prepared by spray pyrolysis method
Yb-doped ZnO thin films were prepared on glass substrates by spray pyrolysis technique in order to investigate the insertion of Yb ions in the ZnO matrix and the related optical properties of the films. The molar ratio of Yb in the spray solution was varied in the range of 0-5 at. %. X-ray diffraction patterns showed that the undoped and Yb-doped ZnO films exhibit the hexagonal wurtzite crystal structure with a preferential orientation along [002] direction. No secondary phase is observed in Yb-doped ZnO films. All films exhibit a transmittance between 75 and 90% in the visible range with a sharp absorption onset about 375 nm corresponding to the fundamental absorption edge at 3.3 eV. The photoluminescence measurements show a clear luminescence band at 980 nm that is characteristic of Yb(3+) transition between the electronic levels (2)F(5/2) and (2)F(7/2). This is an experimental evidence for an efficient energy transfer from ZnO matrix to Yb(3+). Hall effect measurements showed low resistivities and high carrier mobilities which makes these films of interest to photovoltaic devices.This work is supported by the program interdisciplinaire énergie du CNRS Grant No. PE10-2.1.2-2
Hf-based high-k materials for Si nanocrystal floating gate memories
Pure and Si-rich HfO2 layers fabricated by radio frequency sputtering were utilized as alternative tunnel oxide layers for high-k/Si-nanocrystals-SiO2/SiO2 memory structures. The effect of Si incorporation on the properties of Hf-based tunnel layer was investigated. The Si-rich SiO2 active layers were used as charge storage layers, and their properties were studied versus deposition conditions and annealing treatment. The capacitance-voltage measurements were performed to study the charge trapping characteristics of these structures. It was shown that with specific deposition conditions and annealing treatment, a large memory window of about 6.8 V is achievable at a sweeping voltage of ± 6 V, indicating the utility of these stack structures for low-operating-voltage nonvolatile memory devices
Contribution a l'etude du silicium hyperdope obtenu par implantation et recuit par laser pulse : application aux cellules solaires
CNRS T 56493 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc
Films de silicium polycristallin obtenus par cristallisation induite par aluminium et épitaxie (Croissance, caractérisations et cellules solaires)
Dans ce travail, nous avons étudié d abord la croissance du silicium polycristallin (couche germe AIC) sur substrats d alumine ou vitrocéramiques par le procédé de cristallisation induit par aluminium du silicium amorphe. Les études ont concerné la cinétique de croissance de la couche AIC en fonction de plusieurs paramètres expérimentaux (température, temps, épaisseur du film Si amorphe, teneur en hydrogène, ) et la détermination des défauts de structure inter-grains (joints) et intra-grains (macles). En utilisant des verres céramiques, nous avons pu réaliser des films poly-Si à T. Nous avons montré que la densité des macles, en particulier 3, est réduite en diminuant la température de cristallisation. Nous avons également recherché à réaliser des films tampons de type n par surdopage et évaluer leurs efficacités. En variant les conditions expérimentales, des couches n+ avec des concentrations de porteurs libres de 1019 à 6.1020cm-3 et des mobilités de 50-60cm2/Vs ont pu être réalisées sur des couches de 0.20m. Nous avons utilisé deux méthodes de croissance de la couche absorbante: l épitaxie en phase vapeur (VPE) à haute température ou l épitaxie en phase solide (SPE) par dépôt d une couche Si amorphe et recuit. Nous avons particulièrement mis en évidence la formation d une distribution graduelle n+n très souhaitable pour les composants photovoltaïques. Enfin nous avons réalisé des cellules photovoltaïques sur ces matériaux afin de valider leur potentiel pour la future génération de cellules solaires. Nous avons ainsi réalisé des structures de cellules de configuration p+pn+ sur poly-Si de type p mais également des configurations n+np+ sur poly-Si de type n. Nous avons mesuré un rendement de l ordre de 5.5% (6.1% en Sun-Voc et en considérant la surface active), pour les cellules préparées par VPE sur couche tampon n-AIC. Il faut rappeler qu aucun confinement optique ni architecture spécifique n a été utilisé. Les caractéristiques impliquant les mesures des différentes grandeurs des cellules et la réponse spectrale, ont permis une analyse fine des régions de pertes de la conversion.In this work, we have prepared p- and n-type polycrystalline silicon seed layers by aluminum-induced crystallization (AIC) of a-Si on alumina and glass-ceramic substrates, followed by epitaxial thickening using low pressure chemical vapor deposition (LPCVD); and HIT solar cells (Heterojunction with Intrinsic Thin layer) were then fabricated. Polycrystalline silicon layer with quite large grains with an average grain size value of ~260m, that is one hundred times more than thickness of AIC layer (0.20m), can be formed by AIC technique at 475C on glass-ceramic substrate. The preferred orientation is independently from substrate and exchange annealing temperature. The main crystallographic defect is 3 that is reduced by lowering the annealing temperature. We used two methods for the growth of the absorber layer: vapor phase epitaxy (VPE) at high temperature or solid phase epitaxy (SPE) by depositing an amorphous Si layer and following annealing. The grain size conservation for epitaxial layers was observered with that of the underlying AIC poly-Si seed layer. We especially highlighted the formation of a n+n graded structure, which is very desirable for photovoltaic components. Finally, we have made solar cells on these materials to validate their potential for future generation solar cells. In addition to p-type cell (p+pn+), we have prepared for the first time n-type based polysilicon solar cells (n+np+) with AIC approach on alumina substrate. An efficiency of about 5.5% realized in our n-type cells without texturization that should be compared to 3.2% for p-type cells. In addition to cell efficiency, the spectral response of the n-type cell is also much wider than that of p-type cell, over a large part of the spectrum. This lead to an enhancement in Leff for n-type cell (~2.60m) compared to that of p-type (0.90m). Analysis of the best n-type based cells with Sun-Voc apparatus, neglecting therefore the contacts resistivity, led to an efficiency value of 6.1%, showing the potential of the n-type polysilicon solar cells without any optimisation of the hydrogenation step, the heterojunction passivation and junction formation, nor the surface texturing.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF
Transition Energétique
International audienc
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