Gallium nitride films have been grown on (0001) sapphire substrates by chemical beam epitaxy (CBE) using triethyl gallium (TEG) and ammonia(NH3)precursors. Prior to the CBE epi-GaN layer growth, electron cyclotron resonance plasma-assisted metal-organic molecular beam epitaxy was utilized to deposit a nucleation layer at lower temperatures. The crystallinity of CBE-grown GaN films was found to be strongly growth–temperature dependent. The degree of crystallinity was correlated with the surface carbon composition as measuredin situby mass spectroscopy of recoiled ions. The optimum growth–temperature range for CBE GaN growth was found to be between 800 and 825 °C. Within this narrow window, thin films with streaky two-dimensional reflection high-energy electron diffraction patterns and good photoluminescence properties were obtained. The surface rms roughness, as measured by atomic force microscopy, was as low as40 Å/1 &mgr;m2for the highest quality thin films; lattice-resolved images supported the deposition of crystalline GaN revealing hexagonal structures with the spacing anticipated for GaN. ©1997 American Institute of Physics.