Bridgman crystal-growth process

Virtual crystal growth, i.e. numerical simulation of the heat- and mass-transport processes has become a standard tool for the development and optimization of academic and industrial crystal-growth processes [5,18,19]. This holds especially for the optimization of Bridgman-type crystal-growth configurations. A typical crystal growth setup implies a vast variety of coupled and interacting physicochemical processes, which have all to be taken into account as accurately as possible to... 

Now, the influence of convective gas flow on the heat transfer can be estimated for Bridgman-type crystal-growth processes carried out under high gas pressure conditions such as the growth of GaAs (3-7 bar) InP (30-40 bar) and GaP ( 80 bar). Assuming a temperature difference AT between the water-cooled vessel and the outer thermal insulation of the heaters of 100 K and a distance I of more than 5 cm one obtains for a gas pressure p > 1 bar from Eq. (5.3) a Grashof number Gr > 1000 and a Nusselt number Nu 1. 

In the following, typical tasks in the field of optimi2ation of Bridgman-type crystal-growth processes are presented where both, thermal modeling and experimental analysis, contribute. 

The control of the shape of the solid/liquid interface during the whole growth process is, in general, and not only for Bridgman-type crystal-growth processes, of great importance for several reasons ... 

Figure 2. Three spatial scales for modeling melt crystal growth, as exemplified by the vertical Bridgman process. From Theory of Transport Processes in Single Crystal Growth from the Melt, by R. A. Brown, AJChE Journal, Vol. 34, No. 6, pp. 881-911, 1988, [29]. Reproduced by permission of the American Institute of Chemical Engineers copyright 1988 AIChE.

The next step is to produce nearly perfect single-crystal boules of silicon from the ultrapure polycrystalline silicon. Many techniques have been developed to accomplish this, and they all rely on a similar set of concepts that describe the transport process, thermodynamically controlled solubility, and kinetics [8]. Three important methods are the vertical Bridgman-Stockbarger, Czochralski, and floating zone processes, fully described in Fundamentals of Crystal Growth by Rosenberger [9]. 

A similar numerical-based optimization of the cooling phase was performed for the Bridgman-type growth of GaAs in [46]. The reduction of the von Mises stress in the crystal by an improved cooling process was confirmed experimentally [46]. The occurrence of slip lines could be strongly reduced. 

Fig. 12.19 Growth process for homogeneous GalnSb single crystals by vertical Bridgman method with ACRT and periodic solute-feeding schemes.

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