  We report on a strong delay in light propagation through bulk GaN, detected
by time-of-flight spectroscopy. The delay increases resonantly as the photon
energy approaches the energy of a neutral-donor bound exciton (BX), resulting
in a velocity of light as low as 2100 km/s. In the close vicinity of the BX
resonance, the transmitted light contains both ballistic and diffusive
components. This phenomenon is quantitatively explained in terms of optical
dispersion in a medium where resonant light scattering by the BX resonance
takes place in addition to the polariton propagation.
