Formation of Interfacial Layers in LaAlO₃/Silicon during Film Deposition

We have studied the interfacial reactions between amorphous LaAlO₃ thin films and Si substrates, using high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that the interfacial layer between LaAlO₃ film and Si substrate is SiLa_xAl_yO_z. The depth distributions of La, Si and Al chemical states show that the ratio of La 4d_3/2 to Al 2p of the interfacial layer remains unchanged with the depth compared to that of the LaAlO₃ film. Moreover, the Si content in the interfacial layer gradually decreases with increasing thickness of the interfacial layer. These results strongly suggest that the Al element is not deficient in the interfacial layer, as previously believed, and the formation of a SiLa_xAl_yO_z interfacial layer is mainly due to the diffusion of Si from the substrate during the LaAlO₃ film deposition. With the understanding of the interfacial layer formation, ones can control the interface characteristics to ensure the desired performances of devices using high-k oxides as gate dielectrics.