Microcrystalline to nanocrystalline silicon phase transition in hydrogenated silicon-carbon alloy films.

Different classes of interesting materials (such as protocrystalline, microcrystalline and nanocrystalline) have been grown under conditions very near to those for the microcrystalline phase. In spite of the importance of these materials, a clear picture regarding their phase transitions is missing. A smooth transition from the microcrystalline to the nanocrystalline silicon phase, distinctly different from an abrupt order-disorder phase transition, has been demonstrated, for the first time, in hydrogenated silicon-carbon alloy films, prepared from a silane-methane gas mixture highly diluted in hydrogen, by varying the rf power in a plasma enhanced chemical vapour deposition system. The study has also provided the signature of medium range order in hydrogenated silicon-carbon alloy films.