Effect of Nitrogen Partial Pressure on the Microstructure of Epitaxial GaN Films Grown by rf Magnetron Sputtering

Epitaxial Gallium nitride (GaN) films were deposited on c-plane sapphire by rf magnetron sputtering using GaAs target with different percentages (10 - 100 %) of nitrogen in Ar-N-2 sputtering atmosphere at a substrate temperature of 700 degrees C. Powder X-ray diffraction studies show the formation of single phase GaN films, which are practically strain free when grown with 20 - 50 % nitrogen in sputtering atmosphere. The surface morphology of the films was studied by atomic force microscopy and the epitaxial quality of the films was ascertained by high resolution Xray diffraction. The microstructural parameters of the films, such as crystallite tilt, microstrain as well as lateral and vertical coherence lengths were obtained from omega and omega-2 theta scans and the corresponding Williamson-Hall plots. These studies reveal that the surface topography and epitaxial quality of the films depend significantly on the percentage of nitrogen in sputtering atmosphere, with the film deposited with 50 % nitrogen exhibiting substantially superior topography and high epitaxial quality.