The continued scaling of complementary metal oxide semiconductor (CMOS) transistors requires replacement of the conventional silicon gate oxide (SiO2) or oxynitride (SiON) with a higher dielectric constant gate dielectric to minimize the leakage current and to maintain a large capacitance for the drain current control. Among several contenders, the transition metal (TM) and the rare earth (RE) metal oxides specifically hafnium oxide (HfO2) and lanthanum oxide (La2O3), are believed to be the suitable successors of the conventional gate dielectric because of their several promising fundamental properties. However, several shortcomings are found to incur when interfaced with the silicon substrate. In this work we have set out to investigate and correlate the physical properties of HfO2 and La2O3 films to their electrical behavior by studying the material and electrical characteristics of MOS capacitors grown on n-type silicon structures. The conduction mechanisms, charge trapping, flat-band voltage shifts, reliability and defects of the dielectric film as well as the chemical compositions and chemical bondings involved were studied based on electrical and x-ray photoelectron spectroscopy (XPS) measurements which led us to set the optimum processing condition for the dielectrics. It has been found that the reliability of HfO2 samples annealed at 700 0C or 800 0C for a short duration (3 min) is very high, as the stressing induced charge trapping in those samples are minimal. On the other hand the hygroscopic nature of La2O3 has been reported to pose a serious problem in the gate dielectric applications. It has been found that annealing the sample at 600 0C improves the stoichiometry of the as-grown films by removal of the hydroxyl groups and suppressing the oxygen vacancies. Investigation of the film properties on nitrogen (N) and aluminum (Al) incorporation in HfO2 and La2O3 films using plasma immersion ion implantation (PIII) was also carried out. It has been found that regardless of the implantation dose only a trace amount of nitrogen (≈ 3 to 5 %) can be introduced into the metal oxide films using PIII. The nitrogen incorporation in the as-deposited HfO2 and La2O3 films has been found to be mainly due to the filling of O vacancies or removal of the hydroxyl group ions and nitridation of silicide bonds at the metal-oxide/silicon interface. Temperature dependent capacitance-voltage and current-voltage characteristics revealed that even trace amount of nitrogen can significantly reduce both bulk and interface oxide trap densities. In case of aluminum implantation in HfO2 films, even though most of the implanted-Al has been found near the surface, there was significant reduction in both bulk and interface traps improving the insulating properties of the dielectrics. In case of La2O3, it has been found that low amount (≈ 6 %) of aluminum incorporation in lanthana film can suppress the leakage current as well as the oxide traps effectively, whereas, higher concentration (≈ 30 %) of aluminum actually degrades the oxide performance. Therefore, optimization of the implantation dose and also the annealing conditions are mandatory to achieve maximum reduction of the oxide traps and leakage current as prolonged annealing may initiate partial crystallization and hence deteriorate the insulating properties.