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Kalaev V.V.,STR Group Ltd.
International Journal of Heat and Mass Transfer | Year: 2012

Flow and turbulence generation in a cubic cavity filled by the liquid driven by the gas shear stress over a liquid/gas interface are considered. The coupled gas/liquid flow model is formulated to gain basic understanding of gas flow effects on melt convection, heat and mass transfer during crystal growth by the Czochralski and Directional Solidification methods. As in real crystal growth applications, the gas velocity is assumed to be much higher than the liquid velocity. The gas flow is considered to be laminar for both case of laminar and turbulent liquid convection. The flow of liquid is studied to find conditions of liquid turbulent transition at increasing gas shear stress. A novel dimensionless number is proposed and validated to describe the gas shear stress effect on the liquid flow. Engineering applications to control melt flow structure and oxygen transport during silicon crystal growth are discussed. © 2012 Elsevier Ltd. All rights reserved. Source


Demina S.E.,STR Group Ltd. | Kalaev V.V.,STR Group Ltd.
Journal of Crystal Growth | Year: 2011

In the present work, 3D features of melt convection during sapphire growth of 100 mm diameter Cz and of 200 mm diameter Ky crystals are studied. The approach accounting for radiative heat exchange with absorption and a specular reflection in the crystal, which we applied in 2D modeling [13], has been extended to 3D computational domains and coupled to 3D heat transfer in the melt, crystal, and crucible. 3D melt unsteady convection together with crystallization front formation are taken into account within the Direct Numerical Simulation (DNS) approach. Results of 3D modeling are discussed in detail and quantitatively compared to the previously reported data of 2D modeling and experiments [2,3]. It has been found that the features of unsteady melt convection during the "before seeding", "seeding", and "shouldering" growth stages are quite different from each other, which necessitates a flexible control of the radial and vertical temperature gradients in the crucible to provide optimal conditions for stable growth of high quality sapphire crystals. © 2011 Elsevier B.V. All rights reserved. Source


Lundin W.V.,RAS Ioffe Physical - Technical Institute | Nikolaev A.E.,RAS Ioffe Physical - Technical Institute | Yagovkina M.A.,RAS Ioffe Physical - Technical Institute | Brunkov P.N.,RAS Ioffe Physical - Technical Institute | And 6 more authors.
Journal of Crystal Growth | Year: 2012

Possibility of AlN growth by MOVPE in a planetary reactor with high growth rate was investigated. Growth was performed on (0001) Al 2O 3 substrates at the reactor pressure of 100 mbar. It was shown that deposition rate is close to diffusion limit at low NH 3 flows and reduces abruptly above a certain threshold value of NH 3 due to gas-phase parasitic reactions. At constant V/III ratio of 1.5-2, AlN growth rate dependence on TMAl flow was linear and a maximum growth rate of 8.6 μm/h was achieved. Process modeling allowed predicting and explaining the trends related to the onset of parasitic chemistry for various V/III ratios and other growth conditions. Surface morphology planarization was achieved by either (1) NH 3 flow rate reduction or (2) TMGa injection after the layer with thickness of 75-300 nm was grown. The second approach looks more fruitful resulting in atomically flat Al(Ga)N layers with a 2 μm/h growth rate. For the conditions (high temperature, low NH 3 and high H 2 concentration) used Ga acts mostly as surfactant (Ga content in Al(Ga)N is about 3-5%). © 2011 Elsevier B.V. Source


Lobanova A.V.,STR Group Ltd. | Segal A.S.,STR Group Ltd. | Yakovlev E.V.,STR Group Ltd. | Talalaev R.A.,STR Group Ltd.
Journal of Crystal Growth | Year: 2012

Comprehensive model of AlInN Metal-Organic Vapor Phase Epitaxy (MOVPE) accounting for the gas-phase and surface chemistry including parasitic reactions/particle formation is developed. Experimental data and modeling results suggest that as V/III ratio increases from several tens (growth of pure AlN) to several thousands (growth of AlInN), the partial AlN growth rate decreases even in the absence of strong particle formation. This effect is associated with the formation of heavy molecular weight/low diffusivity gas-phase dimer species at high ammonia concentration. At elevated pressures growth rate decreases with pressure at a weakly changing composition, which is related to the gas-phase losses of In- and Al-containing species due to reaction with AlN particles. Model allows the prediction of both the AlInN growth rate and composition versus group-III flow rates, temperature, and pressure. © 2011 Elsevier B.V. Source

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