Space-charge-limited currents in La2O3 thin films deposited by E-beam evaporation after low temperature dry-nitrogen annealing

The electrical characteristics of metal-oxide-semiconductor capacitors with Lanthanum oxide (La2O3) gate dielectrics with 1.1 nm equivalent oxide thickness (EOT) are investigated. La2O3 was deposited by E-beam evaporation on n-Si(100), and annealed at 200 degrees C in dry-nitrogen ex-situ for 5 min. From comparing the leakage currents of as-deposited and annealed oxides, it is shown that the leakage currents of annealed oxide were of two types: low and high leakage currents. The behavior of high leakage currents with applied voltage was similar to that of as-deposited oxide. For the explanation of these two kinds of leakage currents, it is shown that conduction mechanisms strongly related to oxide traps are not responsible for leakage currents, except space-charge-limited current (SCLC). From the applied voltage and temperature dependences of the current of the gate oxide, it is shown that the main conduction mechanisms for the two types of leakage current are SCLC and Schottky conductions at low and high applied voltages, respectively. The dielectric constant obtained from Schottky conduction was 27 and consistent with the C-V result. Based on SCLC theory, trap levels in the oxide band gap composed of both exponential and localized distributions were extracted using the differential method.