The mechanism of Si vapor-phase epitaxial growth is studied by using abnitio molecular-orbital calculations. Since ${\mathrm{SiCl}}_2$ is a dominant species in the thermal decomposition of ${\mathrm{SiH}}_2$${\mathrm{Cl}}_2$, it is considered to be the key adsorbate of the epitaxial growth. Therefore, the potential curves of the ${\mathrm{SiCl}}_2$ and Si cluster (${\mathrm{Si}}_{11}$${\mathrm{H}}_{18}$) system are calculated. In the present calculations, the adsorption of ${\mathrm{SiCl}}_2$ is assumed to occur at the hollow bridge site. Depending on the electronic structures of the hollow bridge site, three different types of potential curves that have a minimum are obtained. The first one corresponds to the chemisorption of ${\mathrm{SiCl}}_2$ in which the electronic structure is closed-shell singlet. The binding energy is calculated to be about 146.7 kcal/mol. The second whose electronic state is triplet has a shallow minimum of about 4.6 kcal/mol. The last one is the potential curve of the charge-transfer state from the cluster to ${\mathrm{SiCl}}_2$, which is considered to be important to enhancement of the growth rate by the emission of ultraviolet lights during the vapor-phase-epitaxy process.

• Received 5 March 1990

DOI:https://doi.org/10.1103/PhysRevB.41.12720