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The requirements of present high-performance power electronic systems are exceeding the power density, efficiency, and reliability of silicon-based devices. Silicon carbide (SiC) is a candidate of choice for high-temperature, high-speed, high-frequency, and high-power applications: it has a wide band gap, high thermal conductivity, high saturated electron drift velocity, and high breakdown electric field. SiC is also hard, chemically stable, and resistant to radiation damage. Despite these desirable electronic properties, SiC-based devices are still facing many performance challenges due to the high density of defect states at the SiC/SiO2 interface. This thesis is dedicated to the first-principles study of defects at the SiC/SiO2 interface through hybrid functionals. We first generate a model structure providing a realistic description of the majority bonding arrangements at the 4H(0001)-SiC/SiO2 interface. The description of the electronic structure of the model through hybrid functionals leads to band offsets in excellent agreement with their experimental counterparts. We then study several semiconductor and oxide defects using spin-polarized hybrid density functionals and identify candidate defects responsible for the high density of interface defects measured in the 4H-SiC band gap. Finally, the possibility of growing epitaxial silicate adlayers on SiC is investigated as an alternative approach to greatly reduce the high density of defect states at the SiC/SiO2 interface.