Analysis of structural and luminescence properties of GaAsN epilayers grown by Molecular Beam Epitaxy (MBE) on GaAs substrates indicates the possibility of fabricating high nitrogen content (x>0.03) alloys. The conventional plasma source design where nitrogen flux is controlled using a manual shutter was first implemented. Significant N contamination of GaAs barrier layers which could severely affect carrier extraction and transport properties in targeted devices was observed via HAADF STEM. In order to overcome these limitations, a gate-valve-activated run-vent design was implemented that allowed the plasma to operate continuously during MBE growth, while N plasma flux changes during growth were monitored. The potential of this design for achieving very sharp switching schemes compatible with the fabrication of complex dilute-nitride quantum well structures, while preventing N contamination of GaAs barriers, was demonstrated via photoluminescence and STEM.