Silicon carbide is the only wide band gap semiconductor that has a native oxide, and a leading candidate for development of next-generation, energy efficient, high power metal-oxide-semiconductor field effect transistors (MOSFETs). Progress in this technology has been limited by the semiconductor-dielectric interface structure and its effect on the inversion layer mobility. The major objective of this work is to study and improve 4H-SiC MOSFET interface structure, defect states and inversion layer mobility on the (11-20) crystal face of SiC (a-face), employing nitrogen and phosphorous...