The growth and the characterization of Al x In 1− x N/GaN ( x>0.75) heterostructures by migration-enhanced metal–organic chemical vapor deposition are optimized through variations in growth temperature and precursor modulation schemes, resulting in high quality films. Al x In 1− x N/GaN heterostructures were characterized by XRD reciprocal space mapping in order to calculate the relative strain to GaN as a function of indium composition. AFM measurements yielded an rms roughness value of ∼4 Å. By controlling indium incorporation, a maximum 2DEG mobility of ∼1270 cm 2/V s, a maximum sheet charge density of ∼4.1×10 13 cm −2, and a minimum sheet resistance of 179.9 Ω/□ were obtained.