Tunneling in sub-5 nm La2O3 films deposited by E-beam evaporation

We investigate the leakage current in ultrathin (sub-5 nm) La2O3 dielectric films deposited on n-Si (1 0 0) substrates by electron-beam evaporation and annealed in situ in ultra-high vacuum conditions. We show that simple tunneling models both for the direct and Fowler–Nordheim conduction regimes can accurately reproduce the measured current–voltage characteristics over a wide voltage range. In the latter regime, it is shown the importance of considering the series resistance effect to account for the shape of the characteristics. We propose a method to obtain the series resistance’s value based on the linearization of the Fowler–Nordheim plot. Some experimental features in combination with an exploratory analysis of the fitting parameters seem to indicate that the current flow through the structure is mostly localized, which is attributed to the existence of thickness non-uniformities in the oxide layer. In addition, we show that the application of electrical stress creates traps or defects within the insulator that leads to a progressive increase of the leakage current and to a change of the dominant conduction mechanism at the lowest biases.