Metal-oxide-semiconductor characteristics of thermally grown nitrided SiO2 (9-11.5 nm) on n-type 4H-SiC at 1175 degrees C in various N2O ambient (1, 10, and 50% N2O mixed with 99, 90, and 50% of high purity N-2 gas, respectively) have been investigated. The chemical composition of oxide-semiconductor interface has been evaluated by X-ray photoelectron spectroscopy. The interfacial layer consists of either silicon oxynitride, silicon nitride, and/or silicon oxide phases that may be segregated or mixed in a single layer. Depending on the percentage of N2O being used, the stoichiometry may vary accordingly. The lowest leakage current density is recorded for thin film oxide grown in 10% N2O and it is limited to an applied electric field of not more than 7 MV/cm. This is attributed to the lowest density value of deep oxide trap in this sample if compared with others. The highest dielectric breakdown field has been obtained for thin film oxide grown in 50% N2O as this sample is having the lowest interface trap density and negative effective oxide charge. The origin of these charges is explained in the text. (C) 2009 Elsevier By. All rights reserved.