FORMATION OF MACRODEFECTS IN SIC

4H- and 6H-SiC boules have been grown by a sublimation process in a RF -heated system. A temperature gradient transports the material from so urce to the seed which is positioned at the coolest place of the cruci ble. The single-crystalline boules sometimes have macrodefects in the region of the seed. These defects are hexagonal tubelike cavities (we call them channels) with a diameter of 10 to 50 micrometers and a leng th up to some millimeters. These channels are parallel to the growth d irection. They start at the seed and end with an enlargement of the ho llow. Several possibilities of formation of such hollows are discussed . The experimental results showed that they are probably originated by secondary evaporation of SiC after the crystal has been grown.