A unique growth mariner for the formation of In(Ga)NAs film on GaAs (10 0) substrate is presented in this paper. The In(Ga)NAs compound alloy is significantly realized when a thin InN film is attempted to be overgrown on an InAs prelayers by metalorganic chemical vapor deposition (MOCVD). High-resolution X-ray diffraction (HRXRD) studies combined with the secondary-ion-mass spectrometry (SIMS) analysis substantially evidence that the interdiffusion of N and As atoms plays a decisive role in the thermodynamically preferable formation of In(Ga)NAs film, where the considerable amount of Ga atoms are revealed to be out-diffused from the substrate. The N composition in the In(Ga)NAs alloy up to 0.18 has been strikingly achieved using ammonia (NH3) as a source of nitrogen. Fourier-transform infrared spectroscopy (FTIR) transmittance measurements reveals that the optical absorption-edge shifted to lower energy with increasing N concentration. Detailed quantitative estimation on the band-gap energies of In(Ga)NAs films has been presented. (c) 2005 Elsevier B.V. All rights reserved.