Nucleation and growth of epitaxial ZrB₂(0 0 0 1) on Si(1 1 1)

The growth behavior of epitaxial ZrB₂(0001) films on Si(111) via the thermal decomposition of the unimolecular precursor Zr(BH₄) ₄ was studied in situ using low-energy electron diffraction and low-energy electron microscopy, and ex situ using cross-sectional transmission electron microscopy and atomic force microscopy. Under appropriate kinetic conditions, epitaxy was achieved in spite of the very large lattice mismatch between ZrB₂(0001) and Si(111). Our study followed the growth from the initial nucleation stage to the final epitaxial film at various growth temperatures. At 900°C, the growth of ZrB₂(0001) proceeded by the nucleation of two-dimensional islands. These islands eventually coalesced to form a smooth film with an RMS roughness of 0.9nm. The interface between ZrB₂(0001) and Si(111) was modeled theoretically and the most favorable interface consisted of the ZrB₂(0001) growing on a Si(111)-(√3×√3)B surface with the Zr-layer nearest to the interface and the B-layer on the top surface.