High-Quality Single-Crystal Piezoelectric Aluminum Nitride Grown on Gallium Nitride Transition Layer on Sapphire Substrate

This paper presents a high-quality single-crystal piezoelectric aluminum nitride (AlN) thin film grown on gallium nitride (GaN) transition layer on sapphire substrate. The Metal-organic Chemical Vapor Deposition (MOCVD) process enables the growth of 500 nm-thick AlN on top of GaN through the rapid exchange of gases in the reactor. As the growth thickness of GaN further increases from 0.5 µm to 3.5 µm, the FWHMs of the (002)-plane XRCs of GaN and AlN both obviously decrease. It indicates that the crystal quality of AlN thin film is improved. Especially, the AlN thin film exhibits a FWHM of 0.16°. Besides, the existence of GaN provides a pathway for the subsequent dissociation of AlN films from the sapphire substrate. Using laser lift-off technology, the GaN with AlN thin film can be transferred from the sapphire substrate under the condition of pulsed laser energy density. Besides, a potential process idea for fabricating single-crystal AlN -based thin film bulk acoustic wave resonator (FBAR) is provided.