A CVD Method of forming gate dielectric thin films on a substrate using metalloamide compounds of the formula M(NR1R2)x, wherein M is selected from the group consisting of: Zr, Hf, Y, La, Lanthanide series elements, Ta, Ti, Al; N is nitrogen; each of R1 and R2 is same or different and is independently selected from the group consisting of H, aryl, perfluoroaryl, C1-C8 alkyl, C1-C8 perfluoroalkyl, alkylsilyl and x is the oxidation state on metal M; and an aminosilane compound of the formula HxSi(NR1R2)4−x, wherein H is hydrogen; x is from 0 to 3; Si is silicon; N is nitrogen; each of R1 and R2 is same or different and is independently selected from the group consisting of H, aryl, perfluoroaryl, C1-C8 alkyl, and C1-C8 perfluoroalkyl. By comparison with the standard SiO2 gate dielectric materials, these gate dielectric materials provide low levels of carbon and halide impurity. Also described is a method of synthesizing an aminosilane source reagent composition, by reacting an aminosilane precursor compound with an amine source reagent compound in a solvent medium comprising at least one activating solvent component, to yield an aminosilane source reagent composition having less than 1000 ppm halogen.