CVD-grown lightly C-doped superlattices with peak C concentrations of 2.1018/cm2 and 2.1019/cm2 were annealed in NH3, N2/H2, N2, and O2 ambient gases to investigate the influence of a range of point-defect conditions on C diffusion at the nanometer scale. C profiles were measured by Secondary-ion mass spectroscopy. The profiles exhibit exponential-like diffusion consistent with a 'long hop' diffusion process with a characteristic migration length λ (=19 ± 3 nm at 850 °C). Within experimental errors the value of λ is the same for all the ambient gases used, whereas the migration frequency g increases by two orders of magnitude as the ambient gas is changed from NH3 ambient (interstitial undersaturation) to O2 ambient (interstitial supersaturation), and decreases as a function of C concentration in the as-grown superlattice. The results confirm that C diffuses predominantly by a kick out mechanism under near-equilibrium diffusion conditions. Initial results support the chemical-pump model for suppression of diffusion in C-doped silicon.