Low temperature plasma deposition of silicon thin films: From amorphous to crystalline

International audienceWe report on the epitaxial growth of crystalline silicon films on (100) oriented crystalline silicon substrates by standard plasma enhanced chemical vapor deposition at 175 °C. Such unexpected epitaxial growth is discussed in the context of deposition processes of silicon thin films, based on silicon radicals and nanocrystals. Our results are supported by previous studies on plasma synthesis of silicon nanocrystals and point toward silicon nanocrystals being the most plausible building blocks for such epitaxial growth. The results lay the basis of a new approach for the obtaining of crystalline silicon thin films and open the path for transferring those epitaxial layers from c-Si wafers to low cost foreign substrates

Thin crystalline silicon solar cells based on epitaxial films grown at 165 °C by RF-PECVD

International audienceWe report on heterojunction solar cells whose thin intrinsic crystalline absorber layer has been obtained by plasma enhanced chemical vapor deposition at 165 °C on highly doped p-type (1 0 0) crystalline silicon substrates. We have studied the effect of the epitaxial intrinsic layer thickness in the range from 1 to 2.5 μm. This absorber is responsible for photo-generated current whereas highly doped wafer behave like electric contact, as confirmed by external quantum efficiency measurements and simulations. A best conversion efficiency of 7% is obtained for a 2.4 μm thick cell with an area of 4 cm2, without any light trapping features. Moreover, the achievement of a fill factor as high as 78.6% is a proof that excellent quality of the epitaxial layers can be produced at such low temperatures

Low Temperature Plasma Synthesis of Nanocrystals and their Application to the Growth of Crystalline Silicon and Germanium Thin Films

International audienceWe summarize our research studies on the synthesis of silicon and germanium nanocrystals and their application to the growth of a variety of thin films, spanning the range from fully disordered amorphous up to fully ordered crystalline. All these films are deposited in a standard radio-frequency glow discharge system at low temperature (~200 °C). We show how the plasma synthesis of silicon nanocrystals, initially a side effect of powder formation, has become over the years an exciting field of research which has opened the way to new opportunities in the field of materials deposition and their application to optoelectronic devices. Our results suggest that epitaxy requires the melting/amorphization of the nanocrystals upon impact on the substrate, the subsequent epitaxial growth being favored on (100) c-Si substrates. As a consequence, the control of the impact energy is a critical aspect of the growth which will require new strategies such as the use of tailored voltage waveforms

Spatiotemporal changes in surface sediment characteristics and benthic macrofauna composition off the Rhône River in relation to its hydrological regime

International audienceThe consequences of changes in the water flow of the Rhône River on surface sediment characteristics and benthic macrofauna composition were assessed within 3 distinct areas: (1) the delta front, (2) the prodelta, and (3) the distal zone. Five stations were sampled during or closely after: (1) an oceanic flood (April 2007), (2) a generalized flood (May 2008), (3) a Cevenol flood (December 2008), and (4) a dry period (July 2011). Measurements of sediment characteristics included granulometry (D0.5), bulk descriptors of sedimentary organics (OC, TN and THAA), descriptors of labile components of sedimentary organics (chloropigments, EHAA), and both descriptors of origin (Chl-b/Chl-a, C/N) and lability (Chl-a/(Chl-a+Phaeo-a), EHAA/THAA) of sedimentary organics. Sediment Profile Images were collected during April 2007, May 2008 and July 2011. Temporal changes in both sedimentary organics and benthic macrofauna were more important in the delta front and the prodelta than in the distal zone. Bulk characteristics of sedimentary organics presented decreasing inshore/offshore gradients during both April 2007 and July 2011 but not during May and December 2008. There were significant temporal changes in EHAA/THAA at all stations. Changes in benthic macrofauna composition differed between: (1) the delta front and the prodelta, and (2) the distal zone. In the former area, the dry period was associated with establishing a mature community characterized by high abundances and species richness. The best description of spatiotemporal changes in benthic macrofauna composition by surface sediment characteristics was obtained using D0.5, Chl-b/Chl-a, Chl-a/(Chl-a+Phaeo-a) and EHAA, which supports the role of the quality of sedimentary organics in controlling benthic macrofauna composition

Characterization of silicon heterojunctions for solar cells

Conductive-probe atomic force microscopy (CP-AFM) measurements reveal the existence of a conductive channel at the interface between p-type hydrogenated amorphous silicon (a-Si:H) and n-type crystalline silicon (c-Si) as well as at the interface between n-type a-Si:H and p-type c-Si. This is in good agreement with planar conductance measurements that show a large interface conductance. It is demonstrated that these features are related to the existence of a strong inversion layer of holes at the c-Si surface of (p) a-Si:H/(n) c-Si structures, and to a strong inversion layer of electrons at the c-Si surface of (n) a-Si:H/(p) c-Si heterojunctions. These are intimately related to the band offsets, which allows us to determine these parameters with good precision

Galactokinase deficiency:lessons from the GalNet registry

PURPOSE Galactokinase (GALK1) deficiency is a rare hereditary galactose metabolism disorder. Beyond cataract, the phenotypic spectrum is questionable. Data from affected patients included in the Galactosemias Network registry were collected to better characterize the phenotype. METHODS Observational study collecting medical data of 53 not previously reported GALK1 deficient patients from 17 centers in 11 countries from December 2014 to April 2020. RESULTS Neonatal or childhood cataract was reported in 15 and 4 patients respectively. The occurrence of neonatal hypoglycemia and infection were comparable with the general population, whereas bleeding diathesis (8.1% versus 2.17-5.9%) and encephalopathy (3.9% versus 0.3%) were reported more often. Elevated transaminases were seen in 25.5%. Cognitive delay was reported in 5 patients. Urinary galactitol was elevated in all patients at diagnosis; five showed unexpected Gal-1-P increase. Most patients showed enzyme activities ≤1%. Eleven different genotypes were described, including six unpublished variants. The majority was homozygous for NM_000154.1:c.82C>A (p.Pro28Thr). Thirty-five patients were diagnosed following newborn screening, which was clearly beneficial. CONCLUSION The phenotype of GALK1 deficiency may include neonatal elevation of transaminases, bleeding diathesis, and encephalopathy in addition to cataract. Potential complications beyond the neonatal period are not systematically surveyed and a better delineation is needed

A potential role for muscle in glucose homeostasis: in vivo kinetic studies in glycogen storage disease type 1a and fructose-1,6-bisphosphatase deficiency

A potential role for muscle in glucose homeostasis was recently suggested based on characterization of extrahepatic and extrarenal glucose-6-phosphatase (glucose-6-phosphatase-beta). To study the role of extrahepatic tissue in glucose homeostasis during fasting glucose kinetics were studied in two patients with a deficient hepatic and renal glycogenolysis and/or gluconeogenesis. Endogenous glucose production (EGP), glycogenolysis (GGL), and gluconeogenesis (GNG) were quantified with stable isotopes in a patient with glycogen storage disease type 1a (GSD-1a) and a patient with fructose-1,6-bisphosphatase (FBPase) deficiency. The [6,6-H-2(2)]glucose dilution method in combination with the deuterated water method was used during individualized fasting tests. Both patients became hypoglycemic after 2.5 and 14.5 h fasting, respectively. At that time, the patient with GSD-1a had EGP 3.84 mu mol/kg per min (30% of normal EGP after an overnight fast), GGL 3.09 mu mol/kg per min, and GNG 0.75 mu mol/kg per min. The patient with FBPase deficiency had EGP 8.53 mu mol/kg per min (62% of normal EGP after an overnight fast), GGL 6.89 mu mol/kg per min GGL, and GNG 1.64 mu mol/kg per min. EGP was severely hampered in both patients, resulting in hypoglycemia. However, despite defective hepatic and renal GNG in both disorders and defective hepatic GGL in GSD-1a, both patients were still able to produce glucose via both pathways. As all necessary enzymes of these pathways have now been functionally detected in muscle, a contribution of muscle to EGP during fasting via both GGL as well as GNG is suggeste

Incentivizing the Dynamic Workforce: Learning Contracts in the Gig-Economy

In principal-agent models, a principal offers a contract to an agent to perform a certain task. The agent exerts a level of effort that maximizes her utility. The principal is oblivious to the agent's chosen level of effort, and conditions her wage only on possible outcomes. In this work, we consider a model in which the principal is unaware of the agent's utility and action space. She sequentially offers contracts to identical agents, and observes the resulting outcomes. We present an algorithm for learning the optimal contract under mild assumptions. We bound the number of samples needed for the principal obtain a contract that is within $\epsilon$ of her optimal net profit for every $\epsilon>0$

Passivation de surface et croissance épitaxiale sur c-Si par voie plasma basse température pour les cellules solaires à haut rendement

This thesis presents a work which has been devoted to the growth of silicon thin films on crystalline silicon for photovoltaic applications by means of RF PECVD. The primary goal of this work was to obtain an amorphous growth on any c-Si surface in order to provide an efficient passivation, as required in heterojunction solar cells. Indeed, we demonstrated that epitaxial or mixed phase growths, easy to obtain on (100) Si, would lead to poor surface passivation. We proved that growing a few nm thin a-Si1-xCx:H alloy film was an efficient, stable and reproducible way to hinder epitaxy while keeping an excellent surface passivation by the subsequent deposition of a-Si:H films. Process optimization mainly based on Spectroscopic Ellipsometry, Effective lifetime measurements (Sinton lifetime tester) and current-voltage characterization led us to demonstrate that it was possible to obtain a-Si:H/c-Si heterojunction solar cells with stable VOC of 710 mV and FF of 76 % on flat (n) c-Si wafers, with solar cells of 25 cm2 whose metallization was realized by screen-printing technology. This work has also demonstrated the viability of a completely dry process where the native oxide is removed by SiF4 plasma etching instead of the wet HF removal. Last but not least, the epitaxial growth of silicon thin films, undoped and n or p-type doped, on (100)-oriented surfaces has been studied by Spectroscopic Ellipsometry and Hall effect measurements. We have been able to fabricate homojunction solar cells with a p-type emitter as well as p-i-n structures with an undoped epitaxial absorber on a heavily-doped (p) c-Si wafers.Cette thèse est le résultat d'un travail dédié à la croissance par PECVD de couches minces de silicium sur des substrats de silicium cristallin pour des applications photovoltaïques. L'objectif premier était d'obtenir une croissance amorphe sur toutes les orientations cristallines possibles afin de passiver efficacement les surfaces de silicium, prérequis indispensable à l'obtention de cellules solaires à hétérojonction efficaces. Nous avons en effet montré qu'une croissance épitaxiale, ou microcristalline, très faciles à obtenir sur (100) conduisait à une piètre passivation. Nous avons aussi montré que faire croître une couche de quelques nanomètres seulement d'alliage a-Si1-xCx:H permettait d'éviter, de manière robuste et reproductible la croissance épitaxiale, tout en permettant d'obtenir des passivations excellentes en déposant ensuite des couches minces d'a-Si:H. Une optimisation principalement basée sur des mesures d'ellipsométrie spectroscopique, de durée de vie effective (Sinton) et de charactéristiques courant-tension, nous ont permis d'obtenir des cellules à hétérojonctions a-Si:H/c-Si de 25 cm2 avec des VCO et des FF stables de 710 mV et 76 % respectivement sur des substrats lisses de (n) c-Si, dont les contacts étaient réalisés par sérigraphie de pâtes d'aluminium à basse température. Ce travail a aussi permis d'apporter la preuve du concept de cellules entièrement réalisées par voie sèche, i.e. dont l'oxyde natif est gravé par un plasma de SiF4 au lieu d'une trempe HF. Enfin, la croissance épitaxiale de couches de silicium, non-dopé et dopé n et p, sur des surfaces orientées (100) a été étudiée par ellipsométrie et mesures par effet Hall. Nous avons été en mesure de produire des cellules cristallines dont l'émetteur de type P était épitaxié ainsi que des cellules de type p-i-n dont l'absorbeur était constitué par une couche non-dopée épitaxiée de silicium, déposé sur un substrat (100) très dopé au bore

Passivation de surface et croissance épitaxiale sur c-Si par voie plasma basse température pour les cellules solaires à haut rendement

This thesis presents a work which has been devoted to the growth of silicon thin lms on crystalline silicon for photovoltaic applications by means of RF PECVD. The primary goal of this work was to obtain an amorphous growth on any c-Si surface in order to provide an ef cient passivation, as required in heterojunction solar cells. Indeed, we demonstrated that epitaxial or mixed phase growths, easy to obtain on (100) Si, would lead to poor surface passivation. We proved that growing a few nm thin a-Si1-xCx:H alloy lm was an ef cient, stable and reproducible way to hinder epitaxy while keeping an excellent surface passivation by the subsequent deposition of a-Si:H lms. Process optimization mainly based on Spectroscopic Ellipsometry, Effective lifetime measurements (Sinton lifetime tester) and current-voltage characterization led us to demonstrate that it was possible to obtain a-Si:H/c-Si heterojunction solar cells with stable VOC of 710 mV and FF of 76 % on at (n) c-Si wafers, with solar cells of 25 cm2 whose metallization was realized by screen-printing technology. This work has also demonstrated the viability of a completely dry process where the native oxide is removed by SiF4 plasma etching instead of the wet HF removal. Last but not least, the epitaxial growth of silicon thin lms, undoped and n or p-type doped, on (100)-oriented surfaces has been studied by Spectroscopic Ellipsometry and Hall effect measurements. We have been able to fabricate homojunction solar cells with a p-type emitter as well as p-i-n structures with an undoped epitaxial absorber on a heavily-doped (p) c-Si wafersCette thèse est le résultat d'un travail dédié à la croissance par PECVD de couches minces de silicium sur des substrats de silicium cristallin pour des applications photovoltaïques. L'objectif premier était d'obtenir une croissance amorphe sur toutes les orientations cristallines possibles a n de passiver efficacement les surfaces de silicium, prérequis indispensable à l'obtention de cellules solaires à hétérojonction ef caces. Nous avons en effet montré qu'une croissance épitaxiale, ou microcristalline, très faciles à obtenir sur (100) conduisait à une piètre passivation. Nous avons aussi montré que faire croître une couche de quelques nanomètres seulement d'alliage a-Si1-xCx:H permettait d'éviter, de manière robuste et reproductible la croissance épitaxiale, tout en permettant d'obtenir des passivations excellentes en déposant ensuite des couches minces d'a-Si:H. Une optimisation principalement basée sur des mesures d'ellipsométrie spectroscopique, de durée de vie effective (Sinton) et de charactéristiques courant-tension, nous ont permis d'obtenir des cellules à hétérojonctions a-Si:H/c-Si de 25 cm2 avec des VCO et des FF stables de 710 mV et 76 % respectivement sur des substrats lisses de (n) c-Si, dont les contacts étaient réalisés par sérigraphie de pâtes d'aluminium à basse température. Ce travail a aussi permis d'apporter la preuve du concept de cellules entièrement réalisées par voie sèche, i.e. dont l'oxyde natif est gravé par un plasma de SiF4 au lieu d'une trempe HF. En n, la croissance épitaxiale de couches de silicium, non-dopé et dopé n et p, sur des surfaces orientées (100) a été étudiée par ellipsométrie et mesures par effet Hall. Nous avons été en mesure de produire des cellules cristallines dont l'émetteur de type P était épitaxié ainsi que des cellules de type p-i-n dont l'absorbeur était constitué par une couche non-dopée épitaxiée de silicium, déposé sur un substrat (100) très dopé au borePALAISEAU-Polytechnique (914772301) / SudocSudocFranceF