  We present an experimental study of the Dynamic Nuclear Polarization (DNP) of
\si{} nuclei in silicon crystals of natural abundance doped with As in the
temperature range 0.1-1 K and in strong magnetic field of 4.6 T. This ensures
very high degree of electron spin polarization, extremely slow nuclear
relaxation and optimal conditions for realization of Overhauser and resolved
solid effects. We found that the solid effect DNP leads to an appearance of a
pattern of holes and peaks in the ESR line, separated by the super-hyperfine
interaction between the donor electron and \si{} nuclei closest to the donor.
On the contrary, the Overhauser effect DNP mainly affects the remote \si{}
nuclei having the weakest interaction with the donor electron. This leads to an
appearance of a very narrow ($\approx$ 3 mG wide) hole in the ESR line. We
studied relaxation of the holes after burning, which is caused by the nuclear
spin diffusion. Analyzing the spin diffusion data with a simple one-dimensional
spectral diffusion model leads to a value of the spectral diffusion coefficient
$D=8(3)\times 10^{-3}$ mG$^2$/s. Our data indicate that the spin diffusion is
not completely prevented even in the frozen core near the donors. The emergence
of the narrow hole after the Overhauser DNP may be explained by a partial
"softening" of the frozen core caused by Rabi oscillations of the electron
spin.
