Plasma enhanced chemically-vapor-deposited silicon-rich oxides (200 Å and 500 Å in thickness) of various excess silicon content were deposited onto thermal silicon dioxide (SiO2) layers (103, 207, and 530 Å in thickness) grown on a p-type silicon (Si) substrate. The dielectric constant, electron injection efficiency, current-voltage (I-V) reproducibility, and breakdown property of these composite structures were examined. The dielectric constants of Si-rich oxide were observed to increase with Si content from 3.8 for films deposited at a gas phase ratio (R0) of the concentration of nitrous oxide (N2O) to silane (SiH4) of 150 to ∼10 for films deposited with R0=0. The Si-rich oxides with R0≤5 were found to work as electron injectors. The average oxide field needed to induce a current of 4.8×10-7 A/cm2 through the SiO2 (530 Å in thickness) decreased about 40% in magnitude by adding a Si-rich oxide layer with the optimized R0(=1) compared to that of a control sample which had no Si-rich oxide layer. For thin SiO2 (103 Å and 207 Å in thickness) samples, the decrease of the average field was only 2% and 10% in magnitude with the optimized R0 (=2) layer, respectively, due to the relatively large voltage drop (≊-1 V) across the Si-rich oxide compared to that across the thermal oxide layer. The voltage drop across the oxide is discussed in terms of a dual dielectric model. The yeild, which was defined as the percentage of capacitors that required a field larger than 2 MV/cm to obtain a current of 9.6×10-4 A/cm2, on as-fabricated samples was larger than 90% for all samples with Si-rich oxide. The samples were not destroyed by the passage of a relatively high current density (1.21×10-2 A/cm2) through the oxide and subsequent measurements resulted in approximately the same field to produce the specified current as for the first measurement. The yield was found to have a maximum at R0=1-10 depending on the thickness of Si-rich oxides and SiO2. Current-voltage reproducibility was also found to be improved by the deposition of Si-rich oxide.