growth of 100 mm GaAs
The computational grid and the temperature distribution in the VCz system for
4" GaAs crystal growth
Numerical analysis of VCz and LEC growth is usually more complicated than
the analysis of conventional CZ growth because of turbulent gas convection
and the presence of encapsulant layer.
The experimental regimes with high crucible rotation rates pose additional
difficulties for numerical treatment because of strong velocity gradients.
Using CGSim software we performed 3D unsteady analysis of experimental regimes
with high crucible rotation rates for 100 mm GaAs VCz crystal growth and studied
the effect of the optical characteristics of the encapsulant on the melt flow
and the crystallization front geometry.
Global heat exchange in the growth system has been simulated using 2D steady
state approach. The computational grid and obtained temperature distribution
in the CI 358 puller modified for 100 mm GaAs VCz growth are shown in Figure 1.
The temperature distributions and the flow patterns obtained in the 2D
computations. The encapsulant is considered an opaque (a) or
transparent (b) medium.
Here we present
computational results for two
cases opposite with respect to the radiative properties of the encapsulant
layer: opaque and completely transparent. Detailed temperature and velocity
distributions for these two cases are presented in Figure 2, where one can see
the effect of the encapsulant optical properties on both the temperature
distribution and the melt flow.
Detailed analysis of heat transfer and melt/encapsulant flows in the
crystallization zone was performed within a 3D unsteady approach. Computations
were coupled with 2D steady computations of the global heat transfer trough
iterational exchange of thermal boundary conditions.
Fig. 3. An example of the
3D block-structured computational grid for crystallization zone.
Fig. 4. The instantaneous
flow patterns obtained in the 3D computations. The encapsulant is
considered an opaque (a) or transparent medium (b).
Comparison of the computed and experimental crystallization front shape.
The encapsulant is considered an opaque (a) or transparent
The results obtained using CGSim
with the account of the turbulent melt convection and the encapsulant flow
are generally in reasonable agreement with the experiment. However, if the
encapsulant is assumed to be opaque, the interface deflection tends to be slightly
overestimated, and vice versa: when encapsulant is simulated as competely
transparent medium the interface deflection is slightly underestimated,
see Figure 5.
1. "3D computations of melt convection andcrystallization front
geometry during VCz GaAs growth",
O.V. Smirnova, V.V. Kalaev, Yu.N. Makarov, Ch. Frank-Rotsch,
M. Neubert, P. Rudolph,
J. Crystal Growth, 266 (2004) pp. 67–73.