An abrupt transition to a 111 faceted growth mode is observed in molecular-beam-epitaxy growth of dilute GaN x As 1x (x0.05) films on 100 GaAs substrates. The faceted growth mode is favored by high growth temperatures, high nitrogen content, and high arsenic flux. The best electronic quality material, as measured by low-temperature photoluminescence, was obtained at high growth temperatures and high arsenic flux without exceeding the threshold for facet formation. The nitrogen content was found to be insensitive to the arsenic flux. © 2001 American Vacuum Society.