Nucleation and growth of epitaxial ZrB 2(0 0 0 1) on Si(1 1 1)

Abstract

The growth behavior of epitaxial ZrB 2(0 0 0 1) films on Si(1 1 1) via the thermal decomposition of the unimolecular precursor Zr(BH 4) 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 ZrB 2(0 0 0 1) and Si(1 1 1). 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 ZrB 2(0 0 0 1) proceeded by the nucleation of two-dimensional islands. These islands eventually coalesced to form a smooth film with an RMS roughness of 0.9 nm. The interface between ZrB 2(0 0 0 1) and Si(1 1 1) was modeled theoretically and the most favorable interface consisted of the ZrB 2(0 0 0 1) growing on a Si(1 1 1)–(√3×√3)B surface with the Zr-layer nearest to the interface and the B-layer on the top surface.