Growth and characterization of ammonia-based metal-organic molecular beam epitaxy (NH3-MOMBE) AlxGa1-xN epitaxial films has been conducted. AlxGa1-xN films spanning the entire range of aluminum compositions were grown on GaN templates. This is the first reported successful growth of AlxGa1-xN via NH3-MOMBE, using triethylgallium (TEGa), triethylaluminum (TEAI) and ammonia (NH3) as the precursors. These films were characterized via optical interferometry (OI), atomic force microscopy (AFM), X-ray diffraction (XRD) and scanning electron microscopy (SEM). High-quality AlxGa1-xN films, as inferred by XRD, are achievable in films without cracking. The catalytic effect of Al on NH3 is found to play a major part in the growth rate of the AlxGa1-xN films. The excessive nitrogen produced through this catalytic effect hinders the growth rate at lower Al composition while increasing the growth rate of Al(x)G(1-x)N (x > 0.4) films. Stress in the deposited films is found to be partially relieved through surface cracking along the < 11 (2) over bar0 > direction in the film. These cracks provide dislocation gettering centers, with the dislocation pit density decreasing with increasing Al composition. A basic understanding on the factors affecting the growth of AlxGa1-xN is determined and will become the basis for further investigations into the optimization of AlxGa1-xN growth. (C) Published by Elsevier B.V.