Nonstoichiometry and nanocrystallization of silicon-rich silicon carbide deposited by chemical vapor deposition

Silicon carbide (SiC) deposited by chemical vapor deposition (CVD) from methyltrichlorosilane (MTS)/H-2 was often found to be silicon-rich and micro- or nanocrystalline. We address here the question whether the excess silicon would be localized inside the small SIC crystals contained in the deposit or not. We performed semi-empirical total energy calculations and free energy estimations which show that excess Si atoms should not be localized inside a finite SiC crystal. This is essentially due to the difference between the Si-Si and Si-C sigma overlaps of sp(3) hybrids for a given nearest-neighbor distance. Comparison of a crystallographic equation with experimental results from CVD materials suggests that the SiC nanocrystals be of maximum size allowing all excess Si atoms to be localized at the border of the crystals, provided that there are no Si crystals in the deposited material.