We have studied exciton localization and delocalization effect in GaNAs/GaAs quantum wells (QWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL) and time-resolved PL measurements. Studied results suggest that

at low temperature and under a conventional CW excitation

measured PL spectra were dominated by localized exciton (LE) emission caused by potential fluctuations in GaNAs layer. However

under short pulse laser excitation

it is different. An extra high-energy PL peak comes out from GaNAs/GaAs QWs and dominates the PL spectra under high excitation and/or at high temperature. By investigation

we have attributed the new PL peak to the recombination of delocalized excitons in QWs. This recombination process competes with the localized exciton emission

which

we believe

constitutes the "Sshaped" temperature-dependent emission shift often reported in ternary nitrides of InGaN and AlGaN in the literature.