The quality of 4H-SiC epitaxial layers have considerably improved in recent years owing to the reduction in the density of many crystallographic defects. Yet, since the size of the active area of power devices is large, the presence of defects in epilayers still hampers device yield. Some extended defects, such as the triangular defect, are commonly found in epilayers and have a substantial influence on device performance. Threading dislocations remain prevalent in epilayers, but our knowledge on their impact on devices is not complete. Moreover, our understating of the relation between the defect microstructure, the electronic structure and the resultant influence on device properties is lacking. The objective of this dissertation was to examine the impact of major extended defects found in current epilayers on device performance, and to characterize their microstructure and electronic-structure to gain an understanding on their behavior in devices.

The presence of the triangular defect on the breakdown and leakage characteristics of junction barrier Schottky diodes was studied and was found to be particularly detrimental to devices. The triangular defect microstructure was determined and correlated to its breakdown and leakage behavior in diodes.

The effects of threading dislocation on the leakage and breakdown characteristics of avalanche photodiodes containing a single dislocation were studied. Both screw and edge dislocations were identified in diodes which exhibited premature breakdown and increased leakage currents compared to diodes free of extended defects. Known leakage mechanisms were examined and their feasibility to explain the measured leakage current caused by the threading dislocations is discussed.

The electronic structure at the dislocation core of threading edge and screw dislocations was studied by means of electron holography. The threading screw dislocations in n-type samples were found to be negatively charged, which indicated the presence of bandgap traps at the core. Holography measurements were performed on multiple dislocations from epilayers with different doping densities. Based on these measurements and using a model of closely spaced traps, the trap density and their ionization energies have been estimated.

The edge dislocation electronic structure was studied under the electron beam induced current technique. The charge collection efficiency contrast as a function of doping density and temperature was explained using a model of core traps forming a single level in the bandgap.