  Thin films of laser molecular-beam epitaxy grown \textit{n}-type Ga-doped ZnO
were investigated with respect to their optical properties. Intense
room-temperature photoluminescence (PL) in the near-band edge (NBE) region was
observed. Moreover, its broadening of PL band was significantly larger than
predicted by theoretical results modeled in terms of potential fluctuations
caused by the random distribution of donor impurities. In addition, the
lineshape was rather asymmetrical. To explain these features of the NBE bands,
a vibronic model was developed accounting for contributions from a series of
phonon replicas.
