Effect of thermal annealing on AlN films grown on sputtered AlN templates by metalorganic vapor phase epitaxy

To obtain low-dislocation-density c-plane AlN on sapphire, we have studied the annealing of AlN films at 1650 °C. We prepared an AlN film with a thickness of 20 nm by radio-frequency (RF) sputtering, on which an AlN epilayer with a thickness of 280 nm was grown by metalorganic vapor phase epitaxy (MOVPE) at different growth temperatures. Finally, the AlN film on sapphire was annealed at 1650 °C. The full width at half maximum (FWHM) of the X-ray rocking curve (XRC) for AlN(0002) was approximately 50 arcsec for all samples, whereas that for AlN() significantly decreased from 6500 to 350 arcsec after thermal annealing. A surface morphology with atomic steps and a terrace structure was clearly observed after thermal annealing. From these results, we concluded that a high-quality AlN film can be obtained by annealing a stacking structure of MOVPE-grown AlN (buffer layer)/sputtered AlN (nucleation layer)/sapphire substrate.