Carbon precipitation in silicon: Why is it so difficult?

It is well-established that oxygen precipitation in silicon occurs readily and is further facilitated by the presence of carbon. In contrast, carbon precipitation in silicon appears to be a difficult process which takes place only in the presence of a sufficiently high supersaturation of oxygen or silicon self-interstitials. It is suggested that a high interface energy of carbon precipitates in conjunction with the volume decrease associated with carbon precipitation or agglomeration allows one to understand the precipitation behavior of carbon in silicon.