Optimization of Bulk Hgcdte Growth in a Directional Solidification Furnace by Numerical Simulation
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insight on the problem, although only estimated temperature boundary conditions on the surface of the ampoule with HgCdTe were available. On the other hand numerical models of the global heat transfer in the AADSF furnace were developed [1,6]. The goal of this work is to match these two approaches and to build complementary models of the heat transfer in the furnace and of the melt convection during crystal solidification. To take full advantage of the AADSF design, the ability to analyze temperature field is of utmost importance. The approach undertaken in the present work is close to that presented by Rosch [6]. However, in addition to conduction, both radiation and convection are directly included here in the numerical model. The programming efforts were significantly reduced due to the use of the commercial finite element package FIDAP [7]. AADSF NUMERICAL MODEL The AADSF furnace design is shown schematically in figure l(b). The design of the furnace includes five independently controlled heating elements to provide the desired temperature profile. Another important feature is the design of a steep temperature gradient zone which includes a booster heater, a heat extraction plate and insert to limit radiation transfer between the hot and cold zones. From a numerical modelling point of view, three typical zones in the furnace can be distinguished. First there is solid HgCdTe along with molten material, where conduction 139 Mat. Res. Soc. Symp. Proc. Vol. 398 01996 Materials Research Society
and convection occur in an area with boundary movement caused by the solidification. There is no radiation in this area as HgCdTe is opaque. Secondly, there are the fused silica ampoule, the surrounding furnace solid opaque parts, and empty cavities in which conduction and radiation are the primary modes of heat transfer. A brief description of the approach to model these two zones follows. Finally as the furnace cavities include argon, convection should be also taken into account. Conduction and radiation in furnace cavities are treated in the same way as in the rest of the furnace, but further details regarding convection in gas are not presented here, due to limited space. Although final results present a steady state temperature distribution, time dependence was included into the model, so that transient calculations cold be performed to obtain a reasonable initial guess of the finite element solution.
.i.
(a)
(b)
Figure 1. (a) Schematic presentation of the AADSF furnace. Details of cartridge design are omitted. (b) Simulated steady state temperature field in the furnace.
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Modelling of Conduction and RadiationA numerical model proposed here is implemented throughout the furnace, as shown in figurel(b). Necessary modifications are included in the area where convection occurs. The modeled area also include heating elements. The temperature of each heating element is controlled via electronic control units to ensure that deviation from the desired set point temperature do not exceed 3.50 K, even for a maximum tem
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