Effect of domain boundaries on the electrical properties of crystalline Gd₂O₃ thin films

We report on the effect of domain boundaries on the electrical properties of epitaxial Gd₂O₃ thin films grown on Si(001) substrates with 4° miscut along [110] azimuth. Dedicated preparation of the substrate surfaces can lead to two different microstructures of epitaxial Gd₂O₃ layers when grown at identical growth conditions. A substrate surface with terraces of biatomic steps height is the key point to achieve single crystalline epitaxial Gd₂O₃ layer. Such epi-Gd₂O₃ layers exhibited significantly lower leakage currents compared with the commonly obtained epitaxial layers with two orthogonal domains. However, for capacitance equivalent thickness below 1 nm, this difference disappears, indicating that for ultrathin layers direct tunneling becomes dominating. Additionally, forming gas annealing can reduce the leakage current by a few orders of magnitude. Here, thinner layers of both structural types exhibited similar electrical properties.