Thermal system design and dislocation reduction for growth of wide band gap crystals

In SiC vapor growth, micropipes and dislocations that originate at the seed/boule interface can continuously propagate into the newly grown crystal and adversely affect the quality of the crystals. The defect density can be reduced by the method of growing a large diameter crystal from a small seed through lateral growth under controlled thermal environment. In this paper, SiC growth processes with varying thermal conditions have been simulated; the shapes of the as-grown crystals are predicted and the thermo-elastic stress fields in the crystals are calculated to describe the dislocation density distributions. The simulation results show that if thermal conditions are properly controlled, it is possible to reduce the micropipe density through lateral growth without increasing basal plane dislocation density. The effects of operational parameters such as the axial and radial temperature gradients and seed mounting technique on the size and quality of the crystals are also investigated. The ceramic polycrystalline material that grows on the crystal periphery is illustrated to jeopardize the quality of the crystals. In addition, the influences of some geometrical parameters on thermal environments in the growth chamber are also analyzed. The current finding can also help in the design of AlN/GaN growth system.