Insights into the nature of SiH₄-BH₃ complex: Theoretical investigation of new mechanistic pathways involving SiH_3. and BH_4. radicals

We have investigated a new type of interaction between silane (SiH₄) and borane (BH₃) using high level ab initio calculations. The SiH₄-BH₃ complex is found to be extremely stable with the formation of a bridged hydrogen bond between SiH₄ and BH₃. Hence, it might have a hitherto unknown role in the mechanism of chemical vapor deposition (CVD), which is employed in the fabrication of boron doped silicon semiconductor materials. In an attempt to unravel this role and the underlying reasons responsible for the stability of this complex, we have carried out a detailed analysis based on the structure and molecular orbitals. The results indicate that the binding strength and electronic character of the bridged hydrogen bond in the SiH₄-BH₃ complex is between those observed in double hydrogen bridged B₂H₆ and mono-hydrogen bridged anion B₂H₇^-. In contrast to B₂H₆ and B₂H₇^-, it should be noted that the complex is stabilized by direct strong electrostatic interaction between the positively charged Si atom and the negatively charged B atom as well as by monobridged hydrogen bonding. Furthermore, we also note that the SiH₄-BH₃ complex would dissociate to form SiH_3. and BH_4. radicals. The existence of this complex is also inferred from good agreement between the calculated IR spectra and experimentally observed spectra of thin solid films of boron doped silicon semiconductor materials.