The influence of temperature on deuterium (or hydrogen) diffusion in GaAsN is investigated by secondary ion mass spectrometry and photoluminescence (PL). Deuterium incorporation at 200°C leads to an extremely sharp D concentration profile, which decreases by a factor of 10 within 5nm. This has great relevance to the attainment of an in-plane band gap engineering of dilute nitrides as demonstrated by PL in ensembles of artificial GaAsN wires.