Effect of domain boundaries on dielectric properties of lanthanide oxide based gate dielectrics

In this work, impact of domain boundaries on dielectric properties of epitaxial Gd₂O₃ thin films grown on Si(001) substrates with 4° miscut along [110] azimuth were studied. Epitaxial Gd₂O₃ layers with and without domain boundaries could be prepared on same Si(001) substrates with 4° miscut when the surface is prepared under special condition prior to the layer growth. A miscut substrate surface with terraces of biatomic steps height could be the crucial point to be succeeded to grow single domain epitaxial Gd₂O₃ layer. Epi-Gd₂O₃ layers without any domain boundaries exhibited significantly lower leakage currents compare to that commonly obtained epitaxial layers with two orthogonal domains. However, for capacitance equivalent thickness below 1 nm, the differences disappear, indicating that for ultra thin layers direct tunneling becomes dominant conduction mechanism. Additionally, a forming gas annealing treatment on these samples could further reduce the leakage current by few orders of magnitudes irrespective of their structure. Here, thinner layers of both structural types exhibited similar electrical properties.