Defect evolution during growth of SiC crystals

SiC single crystals grown by sublimation exhibit relatively high dislocation densities and often contain a network of slightly misoriented grains. In order to understand the evolution of dislocation structures and grain boundaries during growth, we studied wafers sliced from different parts of the sublimation-grown SiC single crystals. The wafers have been characterized using imaging with crossed-polarizing filters, etching in molten KOH, optical microscopy and X-ray rocking curves. It was found that in the growth direction from the seed towards the boule dome the dislocation density decreases and the crystal quality as determined by X-ray diffraction measurements improves, while the cross-polarizer image contrast becomes more pronounced. The observed trends are discussed.