Experimental studies of hollow-core screw dislocations in 6H-SiC and 4H-SiC single crystals

Micropipes or hollow-core screw dislocations are often observed along the [0001] growth axis in both 6H-SiC and 4H-SiC single crystals. The magnitudes of the Burgers vectors of these screw dislocations, b, have been determined using Synchrotron White Beam X-ray Topography (SWBXT). Scanning Electron Microscopy (SEM) readily reveals that micropipes emerge as holes on the as-grown surface, with diameters, D, ranging from about 0.1 to a few micrometers. By correlating topographic images and SEM micrographs, it is confirmed that micropipes are hollow-core screw dislocations with b ranging from 2c to 7c in 6H-SiC (c = 1.512 nm), and from 3c to sc in 4H-SiC (c = 1.005 nm). The b and D values were fitted to Frank's relation for hollow-core screw dislocations(1): D = mu b(2)/4 pi(2) gamma, where mu is the shear modulus, and gamma is the specific surface energy. For both 6H-SiC and 4H-SiC, statistical analysis of the relationship between D and b(2) shows that it is approximately linear with some data scatter. The ratio of constants, gamma/mu, is obtained for both 6H and 4H-SiC.