Growth And Characterization Of Gaalas/gaas And Gainas/inp Structures: The Effect Of A Pulse Metalorganic Flow

GaAlAs/GaAs and GaInAs/InP thick layers, single and multiple quantum wells were grown by atmospheric pressure metalorganic vapor phase epitaxy. Auger electron spectroscopy, wedge transmission electron microscopy, x-ray diffraction, low-temperature photoluminescence, and scanning electron microscopy were used to analyze the crystal quality. These analysis techniques show that layers grown using high vapor pressure metalorganic sources present fluctuations in the ternary alloy composition. We propose that these fluctuations are due to the pulse character of the high vapor pressure metalorganic flow. Bubbling experiments were performed to show the relationship between ternary layer composition fluctuation and the pulse character of the metalorganic flow. High vapor pressure metalorganic source like trimethylgallium presents tens of Angströms growth rate per pulse or bubble whereas a low vapor pressure source like triethylgallium presents few Angströms growth rate per bubble.71117918

Temporal changes in the epidemiology, management, and outcome from acute respiratory distress syndrome in European intensive care units: a comparison of two large cohorts

Background: Mortality rates for patients with ARDS remain high. We assessed temporal changes in the epidemiology and management of ARDS patients requiring invasive mechanical ventilation in European ICUs. We also investigated the association between ventilatory settings and outcome in these patients. Methods: This was a post hoc analysis of two cohorts of adult ICU patients admitted between May 1–15, 2002 (SOAP study, n = 3147), and May 8–18, 2012 (ICON audit, n = 4601 admitted to ICUs in the same 24 countries as the SOAP study). ARDS was defined retrospectively using the Berlin definitions. Values of tidal volume, PEEP, plateau pressure, and FiO2 corresponding to the most abnormal value of arterial PO2 were recorded prospectively every 24 h. In both studies, patients were followed for outcome until death, hospital discharge or for 60 days. Results: The frequency of ARDS requiring mechanical ventilation during the ICU stay was similar in SOAP and ICON (327[10.4%] vs. 494[10.7%], p = 0.793). The diagnosis of ARDS was established at a median of 3 (IQ: 1–7) days after admission in SOAP and 2 (1–6) days in ICON. Within 24 h of diagnosis, ARDS was mild in 244 (29.7%), moderate in 388 (47.3%), and severe in 189 (23.0%) patients. In patients with ARDS, tidal volumes were lower in the later (ICON) than in the earlier (SOAP) cohort. Plateau and driving pressures were also lower in ICON than in SOAP. ICU (134[41.1%] vs 179[36.9%]) and hospital (151[46.2%] vs 212[44.4%]) mortality rates in patients with ARDS were similar in SOAP and ICON. High plateau pressure (> 29 cmH2O) and driving pressure (> 14 cmH2O) on the first day of mechanical ventilation but not tidal volume (> 8 ml/kg predicted body weight [PBW]) were independently associated with a higher risk of in-hospital death. Conclusion: The frequency of and outcome from ARDS remained relatively stable between 2002 and 2012. Plateau pressure > 29 cmH2O and driving pressure > 14 cmH2O on the first day of mechanical ventilation but not tidal volume > 8 ml/kg PBW were independently associated with a higher risk of death. These data highlight the continued burden of ARDS and provide hypothesis-generating data for the design of future studies

Gravure hélicon de l'InP en plasma HBr. Morphologie et caractérisation des défauts de surface

We report the results of InP etching using a helicon discharge plasma. The etched surface morphology and the pattern profiles were examined by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) was used to observe the sidewall damage for anisotropic etching. Auger electron spectroscopy (AES) was used to obtain the elemental composition in the top 20 nm of the etched surfaces and to evaluate the contamination and desorption. We also characterized surface and subsurface damage in InP etched substrates using photoluminescence intensity. Anisotropic submicronic etched patterns with low damage were obtained with high etch rates. However, a significant amorphisation of the sidewalls have been evidenced by TEM.Nous exposons les résultats de l'étude de la gravure en plasma HBr de l'InP en décharge hélicon en fonction de la température du substrat, de l'énergie ionique, de la pression de travail et de la puissance de source. La morphologie de surface ainsi que les profils de gravure sont éxaminés par microscopie à balayage. Les défauts de flancs sont mis en évidence par microscopie à transmission dans le cas de gravures anisotropes de motifs submicroniques. L'analyse Auger ainsi que des mesures de photoluminescence ont été utilisées pour évaluer la pollution, les désorptions sur une profondeur de 20 nm ainsi que les défauts électriques résultants. Des gravures anisotropes à faibles dommages induits ont été obtenues avec des vitesses de gravure très acceptables. Cependant une importance amorphisation des flancs a été mise en évidence

PROBLEM RELATED TO THE MBE GROWTH AT HIGH SUBSTRATE TEM0PERATURE FORGaAs-Ga1-xAlxAs DOUBLE HETEROSTRUCTURE LASERS

L'épitaxie par jets moléculaires à forte température du substrat(TS ≈ 600°C) est désormais de plus en plus utilisée pour obtenir des couchesde GaAs et Ga1-xAlxAs avec de bonnes propriétés électriques et optiques.Dans le cas des doubles hétérostructures lasers, l'optimisation du courant deseuil est obtenue en augmentant TS ; la valeur optimale que nous avons obtenueest de 1,5KA/cm2 une épaisseur de couche active de 0,16 µm. Cependantau-delà d'une valeur critique de TS d'environ 670°C, nous avons observé uneaugmentation de Js puis une disparition de l'émission laser. Cet effet estcorrelé à un problème particulier de la croissance MBE à très forte températurequi sera étudié.The MBE growth at high substrate temperature (TS ≈ 600°C) is now often used to obtain GaAs and Ga1-xAlxAs layers with improved electrical and optical properties. In the case of GaAs-Ga1-xAlxAs DH lasers, the optimisation of the threshold current density is obtained for increasing TS ; the ultimate value we reached is l,5KA/cm2 for an active layer thickness of 0,16µm However above a critical value of TS ≈ 670°C, an increase of Jth is observed until a non laser emission. This behaviour is related to a specific problem of MBE growth at extremely high substrate temperature, that will be described

Electro-mechanical evaluation of multilayer platings for connectors : experiments and modeling

International audienc

RESPECTIVE ROLES OF IMPURITIES AND DEFECTS IN Al/Ga INTERDIFFUSION IN ION IMPLANTED GaAs-AlxGa1-xAs SUPERLATTICES

L'influence des défauts d'implantation, séparés des effets associés aux charges des impuretés, a été étudiée sur l'interdiffusion d'Al/Ga dans des superréseaux (SR) GaAs-Al0. 3Ga0.7As. L'implantation des éléments isoélectroniques 31P+ et 27Al+ ont été effectués dans des SR à deux températures (25°C et 250°C) dans le but d'obtenir différentes densités de défauts pour chaque élément. Les propriétés de ces structures, avant et après recuits à 850°C durant 6 h, ont été évaluées à l'aide de plusieurs techniques d'analyses. Ainsi, nous avons mis en évidence la dépendance d'interdiffusion sur la densité des défauts et la durée de leur recuit.The influence of implant damage, seperated from impurity change associated effects, has been investigated on Al/Ga interdiffusion. Implants of electrically inactive isoelectronic elements 31P+ and 27Al+ were performed in molecular beam epitaxy grown (MBE) GaAs-Al0.3Ga0.7As superlattices (SLs) at two distinct temperatures (25°C and 250°C) to generate different damage densities. Their properties, before and after anneals at 850°C for periods up to 6 h, were evaluated using several characterization techniques. An unambiguous evidence to the implant damage and anneal duration dependent Al/Ga interdiffusion is presented and discussed

Growth and Characterization of Gaalas Gaas and Gainas Inp Structures - the Effect of a Pulse Metalorganic Flow

GaAlAs/GaAs and GaInAs/InP thick layers, single and multiple quantum wells were grown by atmospheric pressure metalorganic vapor phase epitaxy. Auger electron spectroscopy, wedge transmission electron microscopy, x-ray diffraction, low-temperature photoluminescence, and scanning electron microscopy were used to analyze the crystal quality. These analysis techniques show that layers grown using high vapor pressure metalorganic sources present fluctuations in the ternary alloy composition. We propose that these fluctuations are due to the pulse character of the high vapor pressure metalorganic flow. Bubbling experiments were performed to show the relationship between ternary layer composition fluctuation and the pulse character of the metalorganic flow. High vapor pressure metalorganic source like trimethylgallium presents tens of Angstroms growth rate per pulse or bubble whereas a low vapor pressure source like triethylgallium presents few Angstroms growth rate per bubble