Three-step growth of AlN films on sapphire substrates by metal nitride vapor phase epitaxy

Control of the growth process is important for growing high-quality AlN films. In this work, AlN films were grown on c-plane sapphire substrates by metal nitride vapor phase epitaxy (MNVPE). Interlayer was added between the buffer layer and the formal layer, and the effect of the Ⅴ/Ⅲ ratio of the interlayer on the crystal quality, surface morphology and stress evolution of the films were analyzed. An interlayer with proper Ⅴ/Ⅲ ratio can provide a stable transition from 3D growth mode to 2D growth mode, while high Ⅴ/Ⅲ ratio induce film separation. The optimum Ⅴ/Ⅲ ratio for the interlayer was found to be 11050, and the films obtained under this parameter had a FWHM of the (0 0 2) and (1 0 2) reflections were 641 arcsec and 840 arcsec, respectively. The maximum transmission is 88%. And the film separation phenomenon was found on the samples with high V/III ratio in the second step, which was thought to be the result of growing in 3D mode for a long time.