The present work is intended to pilot the possible use of ammonia precursors for the growth of III-V-N alloys with metal-organic vapor phase epitaxy (MOVPE) as opposed to typical growth procedures using dimethylhydrazine. The GaPN alloys are grown by repeated cycles of surface nitridation and growth of a thin GaP layer with an interval separating the nitridation and growth. The effects of conditions and duration of each step on the N composition and crystallinity are systematically clarified. An N composition is controlled up to 1.6% in the current conditions, maintaining a high crystalline quality comparable to the GaP substrates, while a continuous-supply method yields a much lower value.