A new alloy system, the GaN1-xAsx alloys in the whole composition range was successfully synthesized using the non-equilibrium low temperature molecular beam epitaxy method. The alloys are amorphous in the composition range of 0.17 < x < 0.75 and crystalline outside this region. The amorphous films have smooth morphology, homogeneous composition and sharp, well defined optical absorption edges. The bandgap energy varies in a broad energy range from ∼3.4 eV in GaN to∼0.8 eV at x∼0.85. The reduction of the band gap can be attributed primarily to the downward movement of the conduction band for alloys with x > 0.2, and to the upward movement of the valence band for alloys with x < 0.2. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)