Luminescence dynamics for the near-band-edge (NBE) emission peak at around 250 nm of c-plane Si-doped Al0.6Ga0.4N films grown on AlN templates by low-pressure metalorganic vapor phase epitaxy were studied using deep ultraviolet time-resolved photoluminescence and time-resolved cathodoluminescence spectroscopies. For the films with the Si-doping concentration, [Si], lower than 1.9 × 1017 cm-3, the doping lessened the concentration of cation vacancies, [VIII], through the surfactant effect or the aid of the reactant doping in a form of H3SiNH2. However, the room-temperature nonradiative lifetime, and, consequently, the equivalent value of internal quantum efficiency in the weak excitation regime steeply decreased when [Si] exceeded 10 18 cm-3. Simultaneously, the intensity ratio of the deep-state emission band to the NBE emission abruptly increased. Because the increase in [Si] essentially gives rise to the increase in [VIII] (for [Si] > 1.9 × 1017 cm-3) and the overcompensation of Si is eventually observed for the film with [Si] = 4.0 × 1018 cm-3, the formation of acceptor-type native-defect complexes containing Si such as V III Si III is suggested.