Influence of nitrogen flow ratio on properties of c-axis oriented AlN films grown by RF magnetron sputtering

Successful growth of c-axis oriented aluminum nitride (AlN) films with uniform columnar structure on (0006) sapphire substrates by Radio Frequency (RF) reactive magnetron sputtering. In this paper, the crystal structure and morphological characteristics of AlN films were changed by varying the nitrogen (N2) flow ratio in the mixture of N2 and argon (Ar) gas, i.e., N2/(Ar + N2). Transmission electron microscopy and X-ray diffractometer analysis confirmed that the AlN films first formed a buffer layer at the interface and subsequently exhibited a high degree of c-axis orientation. Combined atomic force microscopy and scanning electron microscope tests show that the surface undulations of the AlN films were very small reaching a root mean square (RMS) surface roughness of 0.2750 nm. The X-ray photoelectron spectroscopy spectra confirmed the formation of AlN. Finally, the optical band gap and defect types of the films were determined by ultraviolet and visible spectrophotometry and photoluminescence spectrum.