The formation of threading defects in sublimation grown silicon carbide

The goal of this thesis was to investigate and provide evidence for the mechanisms involved in the formation of threading defects during physical vapor transport growth of Silicon Carbide and using this evidence to adjust growth parameters to decrease the overall density of these defects.; The relationship between seed mounting and the formation of thermal decomposition cavities in physical vapor transport grown silicon carbide was investigated. The seed locally decomposes at void locations and Si-bearing species are transported through the void. The decomposition produces a cavity in the seed; the silicon is deposited on and diffuses into the graphite lid. The formation of thermal decomposition cavities can be suppressed by the application of a diffusion barrier on the seed crystal backside.; The subsurface damage generated by the polishing of silicon carbide crystals was investigated by measuring dislocation densities in sublimation grown SiC layers and high-resolution x-ray diffraction. Physical vapor transport growth on silicon carbide seeds, that are given a typical polishing finish of 1 μm diamond paste, leads to the nucleation of threading edge dislocations on the order of 107 cm−2 and threading screw dislocations in densities on the order of 106 cm−2 .; A possible nucleation mechanism for threading edge and screw dislocations during the physical vapor transport growth of SiC has been investigated. Growth over intentionally deposited carbon inclusions led to an edge and screw dislocation density orders of magnitude higher than the surrounding crystal. This was explained by both the lateral overgrowth of the deposit and the nucleation of material on a second phase precipitate. The sublimation growth of silicon carbide on seed crystals with no surface damage and no surface deposits was investigated. Nucleation of 2D islands on the growth surface lead to deviations in the c-stacking and produced both Frank and Shockley stacking faults. These stacking faults correlate with threading dislocations, acting as the origin of looping dislocation pairs. The growth rate is shown to affect the threading dislocation density. A growth rate of 0.0215 mm/hr produces a crystal with a threading screw dislocation density of only 20 cm−2 while a growth rate of 1.5 mm/hr results in a density of 4 × 10 3 cm−2. (Abstract shortened by UMI.)...