Structural properties of GaN and related alloys grown by radio-frequency magnetron sputter epitaxy

Single-crystalline layers of GaN and related alloys such as AlGaN and InGaN were grown on Al2O3 (0001) substrates by radio-frequency magnetron sputter epitaxy. The crystalline structures of these layers were studied as functions of substrate temperature, N2 composition ratio in N2/Ar mixture source gas and gas pressure during the growth. Surface structure of GaN layer depended on Ga/N ratio in flux density, and nitrogen-rich growth condition resulted in pyramid-type facet structure whereas Ga-rich growth produced flat surface. The crystalline quality of GaN layer improved at relatively low N2 composition ratios, and the GaN layer grown at 30% N2 condition was transparent and colorless. AlxGa1−xN layers with x = 0.06–0.08 and InxGa1−xN layers with x = 0.45–0.5, were obtained at 30–40% and 30–50% N2 composition ratios, respectively. The AlN and InN molar fractions in these layers were considerably different from Al and In molar fractions in starting metal alloys (x = 0.15 in both AlxGa1−x and InxGa1−x alloys).