We have studied the influence of radio-frequency plasma cell operating conditions on the plasma-assisted molecular-beam epitaxy growth of bulk GaAsN and GaInAsN quantum wells. For low N-2 flow rates, the species that mostly incorporate are atoms and the dissociation fraction of N-2 for the lowest flow rate and the highest RF power has been found to be up to 0.7. For high N-2 flow rates, the species that mostly incorporate are vibrationally excited molecules in the N-2 (X, nu) ground state. The vibrational temperature of the N-2 (X, nu) ground state has been found to be higher than 10(4) K. The ion damage has been decreased by increasing the N-2 pressure which induces a decrease of the electron temperature and consequently a decrease of the plasma ionization. Oxygen has been evidenced to incorporate proportionally to nitrogen and its emission line has been identified in the plasma emission spectrum. Finally, quantum-well structures emitting at around 1.3 mum at 300 K have been fabricated and characterized by photoluminescence and photocurrent spectroscopy. (C) 2002 Elsevier Science Ltd. All rights reserved.