Finite Si atom diffusion induced size limitation of self-assembled Si quantum dots (Si-QDs) in silicon-rich silicon carbide (SiC) is demonstrated. After annealing, the Si-QDs with a size of 3 +/- 1 nm are precipitated in the matrix of SiC0.51 deposited by low-temperature plasma-enhanced chemical vapor deposition with Argon-diluted silane and methane mixture. The amorphous-Si dependent Raman scattering peak at similar to 470 cm(-1) is narrowing with increasing temperature, and the Si-CH3 rocking-mode absorption line is shifted by dehydrogenation after high-temperature treatment. The self-assembled Si-QDs in SiC0.51 with a volume density of 4.4 x 10(18) cm(-3) transfer from amorphous to crystalline phase by increasing annealing temperature from 850 degrees C to 1050 degrees C. The calculated Si atom diffusion coefficient of 3-4 x 10(-4) nm(2) s(-1) in Si-rich SiC0.51 is 7 orders of magnitude larger than that in pure SiC, which coincides with the linear extrapolation from pure Si and SiC and reveals nonlinear proportionality with C/Si composition ratio and Si-QD size. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.014202jes] All rights reserved.