Hydrazoic acid, HN3, was shown to be an extremely reactive molecule and an effective precursor species for 'active nitrogen'. At room temperature, hydrazoic acid dissociatively chemisorbed on GaAs (110) surfaces to form the NH radical and N2. At 473 K, the NH fragment reacted with the substrate, broke Ga-As bonds and formed GaN and AsN species. At 673 K, an anionic exchange mechanism commenced; the surface became completely depleted of As and a thin film of GaN formed. When the surface was dosed at 773 K, a 20 Å thick GaN film was grown. This evidence demonstrates that hydrazoic acid is highly reactive at comparatively low surface temperatures and offers a viable alternative to ammonia as a nitrogen precursor gas.