The slightly convex crystallization front is necessary to ensure a bulk single crystal growth and formation of an appropriate surface morphology of SiC crystals . These shape, morphology and the optimal growth conditions of crystallization process allow to obtain crystals with a good quality of the crystalline structure .
The crystallization front is an interface between a solid state and the gas phase, therefore its shape is affected by the temperature distribution in the crystal, and the way of providing of the SiC vapor components. In the SiC crystal growth by physical vapor transport (PVT) method it is a necessary the temperature gradient along the crystal growth direction. In order to obtain crystals with a slightly convex crystallization front there should be also applied the temperature gradient in the perpendicular direction. This shape provides a polytype and doping uniformity and also allows to control the propagation of defects, such as micropipes and dislocations.
In this work we investigate the factors, which can affect the shape of the SiC crystallization front. These factors cause mainly the change of the temperature field in the crystal and its surrounding. The first factor is the way of heating of the growth chamber by the heating system. A commonly used is an inductive or resistive heating, in which there are one or two heating sections. Our experiments have been done in the furnace, which was equipped with two independent resistance heaters. Thus, it was possible to control the axial and radial temperature gradients in the growth chamber during the crystallization processes . The second important factor is an insulation, which is located above the growing crystal. In the experiments there was investigated the influence of the size of the channel through which the heat from the backside of the crystal is radiated. The radial temperature gradient in the crystal can be also affected by placing of the growth chamber in a different place of the heater. There were performed experiments in which the crucible was placed near the bottom of the heater or it was raised by a distance of 7 cm. The temperature and its distribution on the crystallization front may be also affected by the active interaction between the crystal growth surface and SiC source material . There have been done the experiments with a different shape of the source materials and small distances between the crystallization front and the SiC source. Additionally, the effect of the open seed backside method  on the shape of the crystallization front in the first growth stage was investigated.
The aim of our research was to improve the crystallization growth conditions in order to obtain the SiC crystals with a slightly convex crystallization front. This crystal shape ensures a stable growth, in which there is minimalized a risk of polycrystal formation between the SiC crystal and the graphite ring. The lack of polycrystal allows to increase the diameter and the thickness of the obtained SiC crystals. Our works are fundamental studies to develop of the SiC crystallization growth conditions for growth processes, which result in lack of contact between the crystal and the wall of the graphite ring. The obtained SiC crystals will be free from defects and stresses originating from the contact between the crystal and a graphite ring.
Acknowledgements: This work was supported by the SICMAT Project co-financed by the European Regional Development Fund under the Operational Programme Innovative Economy (Contract No. UDA-POIG.01.03.01-14-155/09).
 Z. Herro, B. Epelbaum, M. Bickermann, P. Masri, A. Winnacker, J. Cryst. Growth, Vol. 262 (2004) 105.
 R. Yakimova, M. Syväjärvi, T. Iakimov, H. Jacobsson, R. Råback, A Vehanen, E. Janzén, J. Cryst. Growth, Vol 217 (2000) 255
 K. Grasza, E. Tymicki, K. Racka-Dzietko, M. Orzyłowski, Mater. Sci. Forum 679-680 (2011) 16
 K. Grasza, E. Tymicki, J. Kisielewski, Mater. Sci. Forum, 527-529, (2006) 87
 E. Y. Tupitsyn, A. Arulchakkaravarthi, R. V. Drachev, T. S. Sudarshan, „J. Cryst. Growth 299 (2007) 70.