Growth spirals and polytypism of silicon carbide crystals

Abstract

The different growth features observed on the faces of silicon-carbide (Si-C) crystals are illustrated and explained. These can be divided into (A) Growth Spirals, which are of three types (1) Elementary spirals, with step heights equal to the size of the X-ray unit cell, (2) spirals originating from dislocations of multiple strength, the step heights being a multiple of the X-ray unit cell, (3) interlaced spirals in which the step heights are a fraction of the unit cell. The microscopic studies illustrate the information about the shape of the spirals, interaction of the growth fronts and the growth pattern for a number of dislocations, density of dislocations etc. The interferometric studies of the measurement of step heights lead to an understanding of polytypism of silicon-carbide crystals. (B) Oriented overgrowths, which consist of either oriented triangular pyramids of heights up to a few wavelengths of light or oriented triangular and hexagonal molecular layers. (C) Holes, Hollows and Spots. Holes at the origin of the spirals and certain other spots observed on the step lines are illustrated.