Silicon carbide possesses oustanding properties such as a wide band-gap, high thermal conductivity, good chemical stability and high saturated electron drift velocity that constitute such a significant improvement over conventional semiconductor materials that many potential applications are envisaged. However, while some applications have already been realized, issues relating to crystalline defects remain a barrier to the successful realization of several others. The central focus of this thesis is to study defect structures in SiC bulk crystals, epilayers and devices using synchrotron x-ray topography as well as other characterization techniques. The goals of the studies are to understand the behavior and nucleation mechanisms of various defects and their mutual interactions in SiC bulk crystals, epilayers and devices so as to design strategies to mitigate their negative effects by either reducing their densities or completely eliminating them. The following in-depth studies have been carried out: I. Chemical vapor deposition growth and characterization of silicon carbide homo-epitaxial layers. Homo-epitaxial silicon carbide layers were grown by low pressure chemical vapor deposition using halide precursors. Growth processes were carried out using different growth parameters, e.g., temperatures and gas flow rates. Thermodynamic process was studied using a simple equilibrium model. The surface morphology and defect structures in the grown epilayers were investigated using scanning electron microscopy, optical microscopy, high-resolution x-ray diffraction and x-ray topography. II. Investigation of the interactions between basal plane dislocations and threading dislocations and the formation mechanisms of low angle grain boundaries. The interactions between basal plane dislocations and threading dislocations as well as the formation mechanisms of low angle grain boundaries were studied using synchrotron white beam x-ray topography. The threading screw dislocations act as effective pinning points for the basal plane dislocations, while the threading edge dislocations do not. Threading edge dislocation walls act as obstacles for the glide of basal plane dislocations and aggregation of basal plane dislocations is observed. Interactions between the distributions of basal plane dislocations can induce the formation of low angle grain boundaries. Two cases were observed: (1) where edge type basal plane dislocations of opposite sign are observed to aggregate together to form basal plane tilt boundaries and (2) where similar aggregation occurs against pre-existing prismatic tilt boundaries thereby contributing some basal plane tilt to the boundaries. III. Investigation of the interaction between advancing Shockley partial dislocations and threading dislocations in silicon carbide bipolar devices. The interaction between the advancing Shockley partial dislocations and threading dislocations in silicon carbide bipolar devices was studied and a novel interaction mechanism was proposed. The advancing Shockley partial dislocations are able to cut through threading edge dislocations without generating any trailing dislocation segments. However, when the advancing Shockley partial dislocation encounters a threading screw dislocation, a prismatic stacking fault is nucleated via the cross-slip and annihilation of partial dislocation dipole. This configuration is sessile and precludes the further formation of double stacking faults which would be even more detrimental to device performance than the single stacking faults. IV. Determination of the dislocation sense of micropipes. The dislocation sense of micropipes has been studied. The ray-tracing...