NONSTOICHIOMETRY AND NANOCRYSTALLIZATION OF SILICON-RICH SILICON-CARBIDE DEPOSITED BY CHEMICAL-VAPOR-DEPOSITION

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