Effect of growth stoichiometry on the structural properties of AlN films on thermally nitrided sapphire (1120)

High-quality AlN epilayers were grown via pulsed sputtering deposition on thermally nitrided sapphire $(11\bar 20)$ with precise control of the N/Al ratio. Under slightly Al-rich growth conditions, the growth of AlN epilayers on the thermally nitrided sapphire proceeded in a two-dimensional mode from the initial stage of growth, and their surfaces were atomically flat stepped and terraced structures. The FWHM values of the X-ray rocking curves were as low as 87 arcsec and 339 arcsec for the 0002 and $1 \bar 102$ diffractions, respectively, at a film thickness of 400 nm. The present approach is therefore quite promising for the low-cost fabrication of AlGaN-based UV optical devices.