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West University of Timisoara |
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Blv. V Parvan 4, Timisoara 300223, Romania http://www.uvt.ro |
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Research Project ID_131, 2009-2011 Modeling of the Dewetted Bridgman crystal growth process - control of the monocrystal shape and dopant distribution |
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PROJECT OBJECTIVES
The open problems of the Dewetted Bridgman crystal growth process are the followings: (1) Who are the semiconductors which can be grown using dewetted Bridgman method? (2) Who are the adequate materials used for manufacturing of the ampoule? (3) Which is the optimal furnace configuration? (4) Which is the influence of each process parameter on the stable growth possibility? (5) Who are the optimal process parameters able to control the crystal diameter (constant gap)? (6) Which is the contribution of each process parameter in the dopant distribution? (7) Which is the influence of the external fields (ex. magnetic filed) on the meniscus shape and implicitly on the crystal diameter? For answering of these problems, the research implies: (a) Stability and control of the crystal’s shape; (b) Control of the dopant (impurity) distribution; (c) Experiments; (d) Validation. The first two tasks (a)-(b) will be achieved in this project through qualitative and numerical studies of nonlinear systems of ordinary and partial differential equations which allow the prediction of the shape and of the compositional uniformity. In order to compare numerical results with experimental data, for improving simultaneously and feeding each others, international experts are involved: Prof. Thierry Duffar from Institut National Polytechnique de Grenoble (INPG), Science et Ingenierie des Materiaux et Procedes (SIMAP) laboratory. Experiments are made under others research project finaced by European Space Agency (ESA) and French Space Agency (CNES). For this aim, the following objectives will be achieved: (O1) identification of the nonlinear system of differential equations and the initial conditions which allow the prediction of the gap thickness; (O2) identification of the system of partial differential equations and the boundary conditions which allow the prediction compositional uniformity in the crystal; (O3) development of a set of qualitative and numerical information about the solutions of these systems, following feedback with experimental data; (O4) improvement of the obtained models taking into account supplementary phenomena which take place during the growth process, such that the models to reflect very good the real experiments; (O5) establish the dependence of the solutions of the systems on the process parameters, in order to control the growth process and dopant distribution, and on this base, to elaborate improvements of the production technology. The multi-disciplinary and technologic nature of this work will imply a permanent comparison between numerical results and experimental data. Moreover, under research projects of the French laboratory SIMAP, a new set-up will be built on the basis of Patent certificate: T. Duffar, A. Gagnoud, Procede et dispositif de fabrication de monocristaux, Patent FR2865740AN2005: 901618, and new experiments will be performed under appropriate magnetic field.
The potential contributions in this project are : · The detailed elaboration of the model which allow the prediction of the form of the crystal in the case of the growth by the DW method; Detailed elaboration of the model which allows the prediction of the compositional uniformity in the case of DW method. The first contribution is based on the solid experience of the Principal Investigator in mathematical and numerical modelling of the other crystal growth process without contact with the ampoule walls: Edge-defined film-fed growth (EFG). The second contribution represents a development of the subject included in the NATO project Evaluation and control of impurities in rapid-detection sensors (EAP.CLG. 982530/2007-2008, PI from partner country: Liliana Braescu, PI from NATO country: Thomas F, George, Office of the Chancellor, University of Missouri - St. Louis, St. Louis, MO 63121, USA).
Original aspects: · The identification of adequate boundary conditions of the nonlinear system of ordinary differential equations, in the case of the DW growth method in terrestrial conditions. The numerical integration and the prediction of the form of the meniscus and of the crystal. · The identification of the boundary conditions and of the adequate initial conditions of the system of partial differential equations, in the case of DW. The numerical integration and the prediction of the impurity distribution. The determination of the stationary solutions and analysis of the stability. The determination of the stable growth regions and of the stable growth paths, in the case of the asymptotic stability; the determination of the control functions for obtaining the automatic control of the growth process.
The impact of the contributions: By the accomplishment of the contributions it will be possible to evaluate of the contribution of each process parameter in the dopant distribution. These allow: the determination of the process parameters which optimize the compositional uniformity, the determination of the limits of the EFG growth system, the identification of some technological modifications which should be made in the system. It becomes clear in which measure, each process or material parameter influences the stable growth possibility in DW system. This allows the determination of the limits of this growth system and can suggest possible modifications in the system for improving of the technology. |
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Research Team Principal Investigator: Assoc. Prof. Liliana BRAESCU Experienced researchers: Early stage researchers: Lecturer Iosif Petru BIRTEA PhD Student Simona EPURE Lecturer Bogdan CARUNTU PhD Student Simina MARIS |