Effects of mean free path on the preferentially orientated growth of AlN thin films

AlN thin films grown respectively with (1 0 0) and (0 0 2) orientations were prepared by radio frequency (RF) magnetic sputtering method, under different working pressure or substrate-target distance. The thin films were characterized by X-ray diffraction (XRD). Effects of the mean free path of Al atoms, correlated with the working pressure and target-substrate distance, on the preferentially orientated growth of AlN thin films were investigated in detail. It was observed that when the ratio of the mean free path of Al atoms to the substrate-target distance (R=λ/d) was less than 0.14, the thin films were (1 0 0) preferentially orientated.