CVD grown silicon thin films with high carbon concentration: morphology and self-assembly controlled by surface segregation

We report on unusually high concentration of carbon atoms in crystalline si licon films grown by chemical vapor deposition (CVD). Films with concentrat ion higher than 10% are readily grown by supersonic free jet of disilane an d organometallic molecules. The film quality varies from nearly single crys talline to polycrystalline depending on the growing conditions. Carbon atom s forced to exist in excess of its solubility in crystalline silicon seem t o segregate to the surfaces by exhibiting abnormally high rate of diffusion compared to the reported values of bulk diffusion constants. This property is potentially useful in the fabrication of nanoscale modulations of carbo n concentration profiles. These high carbon concentration regions consist o f nanocrystalline particles of Si oriented a little off the host Si crystal directions. This phenomenon resembles nano-sized island formation in Ge/Si heterogeneous systems often used in quantum dot fabrication, and raises th e possibility of quantum dot formation in this system. (C) 2001 Elsevier Sc ience B.V. All rights reserved.