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Saint-Martin-Vésubie, France

Duffar T.,SIMAP EPM
Crystal Research and Technology | Year: 2011

A thermodynamic study is performed for the systems (Ga or In)-Sb-O-Si in order to better understand the difference observed during dewetting experiments of GaSb and InSb in silica ampoules. Results show that the melts can be considered as non reactive toward silica. When the atmosphere is clean (≤ 1 ppm O;bsubesub), no oxide is formed, while, under oxidising atmosphere, oxides exist above the melting point of the antimonide and are known to increase the wetting angle of the melt on the crucible. However the temperature range for oxide stability is smaller in the case of InSb and this may explain why dewetting is easy for GaSb in presence of oxygen, while it is difficult for InSb. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Sylla L.,Cyberstar | Duffar T.,SIMAP EPM
Journal of Crystal Growth | Year: 2011

A series of experiments was performed in order to look at the solidliquid interface and meniscus region in dewetted Bridgman growth of GaSb and InSb in silica crucibles. In agreement with theoretical models, they show that a very stable dewetting was obtained for GaSb only if an oxidising atmosphere is present in the ampoule, and that it increased the wetting and growth angles. Stable dewetting of InSb was never obtained, which can be explained by wetting and thermodynamic considerations. Experiments with an easily dissolved gas (H2) have shown that a model of dissolutionrejection of ampoule gas cannot explain dewetting. Also the formation of hillocks has been observed. Finally, the self-stabilisation of the gas pressure difference is confirmed but remains largely unexplained. © 2011 Elsevier B.V.


Duffar T.,SIMAP EPM | Bochu O.,French Atomic Energy Commission | Dusserre P.,French Atomic Energy Commission
Journal of Materials Science | Year: 2010

In order to better understand the BGO-crucible interaction, the wetting of the molten BGO on Ir substrates has been studied by the sessile drop method at 1050 °C. It was found that the oxygen partial pressure in the surrounding atmosphere is an important parameter. For PO2 > 0.1 mbar, full wetting is observed without any visible contact angle. X-ray diffraction analyses have shown that Bi2Ir2O7 is formed at the interface. For PO2 lt; 0.1 mbar, a drop is observed with a contact angle of 70° and no chemical reaction is detected. Attempts to grow BGO samples under low oxygen partial pressure resulted in ingot without sticking with the crucible. © 2009 Springer Science+Business Media, LLC.


Stelian C.,SIMAP EPM | Stelian C.,West University of Timisoara | Duffar T.,SIMAP EPM
Journal of Crystal Growth | Year: 2014

Numerical modeling is used to investigate CdTe crystallization by Traveling Solution Growth (TSG) technique under terrestrial and microgravity conditions. Numerical results are compared to some experimental observations on CdTe growth by a TSG seeded process under ground conditions. It is found that the instability of the growth interface is related to the compositional non-uniformities of the liquid zone near the solidification front, caused by the species convective transport from the dissolution interface to the growth interface. The modeling of the ground experiment shows a large liquid zone (approx. 5 cm) after the dissolution of CdTe feed material into tellurium. The convection is characterized by a two-cell pattern. The vortex located near the dissolution interface mixes the solute in this region, reducing the tellurium transport to the growth interface. The interface is more stable in this case, but the dopant (indium) distribution is not homogeneous in the solidified sample. Numerical simulations performed by reducing the length of the liquid zone (approx. 2.5 cm) show one single vortex which is extended in the whole melt volume. The intense convection accelerates the tellurium transport to the growth interface, which is destabilized. In order to avoid the morphological destabilization of the growth interface, crucible rotation at constant speed can be applied. In this case, the homogeneity of dopant distribution in the solidified ingots is significantly improved. The modeling of CdTe crystallization under microgravity conditions shows favorable conditions for the growth with a stable interface in the absence of the convection. © 2014 Elsevier B.V. All rights reserved.


Stelian C.,SIMAP EPM | Duffar T.,SIMAP EPM
Journal of Crystal Growth | Year: 2015

The influence of rotating magnetic fields (RMF) on species transport and interface stability during the growth of Cd0.96Zn0.04Te:In crystals by using the traveling heater method (THM), under microgravity and terrestrial conditions, is numerically investigated. The numerical results are compared to ground and space experiments. The modeling of THM under ground conditions shows very deleterious effects of the natural convection on the morphological stability of the growth interface. The vertical flow transports the liquid of low Te concentration from the dissolution interface to the growth interface, which is consequently destabilized. The suppression of this flow, in low-gravity conditions, results in higher morphological stability of the growth interface. Application of RMF induces a two flow cell pattern, which has a destabilizing effect on the growth interface. Simulations performed by varying the magnetic field induction in the range of 1-3mT show optimal conditions for the growth with a stable interface at low strength of the magnetic field (B=1mT). Computations of indium distribution show a better homogeneity of crystals grown under purely diffusive conditions. Rotating magnetic fields of B=1mT induce low intensity convection, which generates concentration gradients near the growth interface. These numerical results are in agreement with experiments performed during the FOTON M4 space mission, showing good structural quality of Cd0.96Zn0.04Te crystals grown at very low gravity level. Applying low intensity rotating magnetic fields in ground experiments has no significant influence on the flow pattern and solute distribution. At high intensity of RMF (B=50mT), the buoyancy convection is damped near the growth front, resulting in a more stable advancing interface. However, convection is strengthening in the upper part of the liquid zone, where the flow becomes unsteady. The multi-cellular unsteady flow generates temperature oscillations, having deleterious effects on the growth process. © 2015 Elsevier B.V. All rights reserved.

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