Distinct orientation of AlN thin films deposited on sapphire substrates by laser ablation

Abstract.

Crystalline, 50–1200 nm thick aluminum nitride (AlN) films were deposited on sapphire by laser ablation of sintered AlN targets. On c-, r-, m-, and a-cut sapphire the AlN films were (00.1), (11.0), (10.0), and (00.1) oriented, respectively. X-ray diffraction goniometry revealed the in-plane orientation of AlN on c-, r-, and m-cut sapphire to be c: AlN[1000]||Al₂O₃[2100], r:AlN[2010]||Al₂O₃[1000], and m: AlN[0100]||Al₂O₃[0001]. TEM showed a smooth surface of AlN(11.0) grown on r-cut sapphire in contrast to a rough surface and columnar structure of AlN(00.1) films on c-cut sapphire. AFM revealed atomically flat films at initial stages of film growth independent of the substrate orientation. Thick AlN films on c-cut sapphire were rough whereas those on r-cut sapphire remained smooth up to 1 μm thickness with a rms-roughness as low as 1 nm.