Cubic GaN films have been grown on (0 0 1) GaAs substrates by using RF plasma assisted gas source MBE. The cubic GaN films were deposited at different Ga-flux to N-flux ratios that were determined by deposition rates directly. Three growth regimes are defined in the cubic GaN growth diagram. The optical quality of these films was measured by photoluminescence (PL). Micro-Raman scattering was performed to analyze the crystallization of the films The optimal flux ratio for cubic GaN grown at T-S = 720degreesC is on the boundary between intermediate Ga stable regime and Ga droplet regime. (C) 2002 Elsevier Science B.V. All rights reserved.