Effect of sputtering power on surface characteristics and crystal quality of AlN films deposited by pulsed DC reactive sputtering

Aluminum nitride (AlN) is a promising material for use as a substrate for AlGaN-based ultraviolet LEDs and piezoelectric devices. Among the sputtering methods, pulsed DC sputtering provides a superior growth rate and dense AlN films because of the promotion of two-dimensional growth. In this study, the effect of sputtering power on surface characteristics, crystal quality, and residual stress of AlN films deposited by pulsed DC reactive sputtering on a nitrided sapphire substrate was investigated. The homoepitaxial growth of AlN films on this substrate gives high crystal quality compared with the use of other substrates such as sapphire or Si for heteroepitaxial growth. Surface damage on the AlN films increased with an increase in sputtering power, leading to a rough surface. At all sputtering powers, c-axis oriented AlN films were obtained in this study. From the difference in lattice constant compared with the AlN bulk, the inplane compressive stress of the AlN sputtered films was confirmed as residual stress. Residual stress in the AlN films was mostly caused by a peening effect rather than a thermal expansion coefficient difference. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim