The growth of pinhole-free epitaxial DySi_2-x films on atomically clean Si(111)

The growth of pinhole-free epitaxial DySi_2-x films on atomically clean Si(111) has been achieved by depositing a 2-nm-thick Dy layer onto Si(111) with a 1.5-nm-thick capping amorphous Si (a-Si) layer at room temperature followed by annealing at 700 °C in ultrahigh vacuum. The thickness of the a-Si was selected to be such that the consumption of Si atoms from the substrate is minimized by taking into account the formation of an amorphous interlayer at the Dy/Si(111) interface. Based on our experimental findings, a new mechanism for the formation of pinhole is proposed. The Stranski-Krastanov growth behavior of epitaxial DySi_2-x on Si(111) by solid phase epitaxy leads to the apparently random formation of a high density of recessed regions at the initial stage of silicidation. Polycrystalline DySi_2-x was found to be present at the areas inside and epitaxial DySi_2-x outside the recessed regions. Large numbers of Si atoms from the substrate can therefore diffuse through the recessed regions. As a result, the depth and size of the recessed regions increase with annealing time. Finally, the DySi_2-x thin layer inside the recessed regions with higher interface energy is thermally unstable and breaks apart to form pinholes.