Highly strained InxGa1-xP1-yNy/GaP1-zNz quantum wells (QWs) with direct transition (x > 27%) were grown on GaP (100) substrates by solid-source molecular beam epitaxy (SS-MBE). The interfaces of In0.33Ga0.67P0.98N0.016/GaP0.988N0.012 QW were smooth and straight. However, the interfaces of In0.45Ga0.55P0.98N0.02/GaP0.984N0.016 QW were roughened showing well-width fluctuations. From our experimental and calculated results, the conduction band offsets were very small for both the InGaPN/GaPN QWs grown on GaP substrates. The photoluminescence (PL) of the InGaPN/GaPN QWs could be based on the recombination between electrons in the conduction band and holes at the first quantum level in the valence band. Rapid thermal annealing at 800 degrees C for 30 s in a N-2 ambient improved the integrated PL intensity by a factor of 3 with a red-shift. This improvement in optical properties could be attributed to annihilation of N-related defects through atomic rearrangement. The highly strained In0.33Ga0.67P0.984N0.016/GaP0.988N0.012 QW was maintained after thermal annealing below 800 degrees C for 30 s, although the local atomic rearrangement could occur. (c) 2006 Elsevier B.V. All rights reserved.