Long range order in AlxGa1−xN films grown by molecular beam epitaxy

The first observation of atomic long range ordering in ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ thin films grown by electron cyclotron resonance assisted molecular beam epitaxy on sapphire and 6H-SiC substrates is reported. The phenomenon was investigated by studying the superlattice peaks (0001), (0003), and (0005) using x-ray diffraction. The relative intensity of these peaks was found to be largest for Al content in the 30%–50% range in qualitative agreement with expectations for an ordered structure of ideal ${\mathrm{Al}}_{\mathrm{0.5}}{\mathrm{Ga}}_{\mathrm{0.5}}\mathrm{N}$ stoichiometry. The average size of the ordered domains in the films was found to be within a factor of 4 of the films’ thicknesses. The degree of ordering depends on the III/V flux ratio and exhibits a weaker dependence on Si doping.