InNAs has been grown by low-pressure metalorganic chemical vapor deposition on vicinal GaAs(1 0 0) substrates misoriented by 2 degrees towards [0 0 1]. In situ plasma-generated arsine radicals were employed for the first time to achieve high source flux ratio of N/As, with the aim of synthesizing InNAs with a high solid-phase nitrogen composition. The in situ generated arsine is produced by placing solid arsenic downstream of a microwave hydrogen plasma. Nitrogen cracked by microwave excitation, and trimethylindium feedstock carried by hydrogen gas were used as the other sources. The grown InNAs is always accompanied by hexagonal InN, while the nitrogen composition of the InNAs varies with changing growth conditions. A small amount of cubic InN also occurs in the grown films at low nitrogen radical flow. The growth mechanism and the key pathways for synthesis of InNAs single crystal films are discussed.