An example of a highly disordered SiC crystal (J59), illustrated by extensive streaking along the diffraction rows.

(a) A full plate topograph containing principally the 6H and 15R polytypes although there are some disordered layers & long period polytypes present. In the former case there is streaking visible along the 314l row and in the latter case some feint reflections between the shorter period polytypes. The measured thickness of the 15R and 6H polytype reflections are 530 m m and 120 m m respectively totalling 650 m m.

(b) A 4150 central reflection, containing all the polytypes, has a measured total crystal thickness of 950 m m which can not be accounted for by the 6H and 15R polytypes alone. Heavy defect density bands are also present and are visible at the boundaries between the 15R/6H polytypes and the 6H/LPP/1DD layers. These have been a commonly found occurrence in this survey as is illustrated in table 3.

(c) A model to scale of the measured polytypes and the unaccounted for LPP/1DD layers of ~ 300 m m thickness forming a rarely found open sandwich configuration (see figure 8).