Effect of AlN buffer on the properties of AlN films grown on sapphire substrate by MOCVD

We presented a study on the effects of low-temperature (LT) AlN buffer growth time and surface morphology on the properties of high-temperature (HT) AlN epitaxial films using metal-organic chemical vapor deposition. Atomic force microscopy, Double crystal X-ray diffraction, Raman test and optical transmission measurement were employed to characterize the four HT AlN samples with different LT AlN buffer growth time. The results demonstrate that the LT AlN buffer growth time and surface morphology are key parameters for the quality of the HT AlN films. With an optimized LT AlN buffer growth time of 6 minutes, a 1-μm-thick high-quality and crack-free AlN film was obtained. The full width at half-maximum of X-ray diffraction (0002) and (1012) rocking curves of the AlN film are 42 and 530 arcsec, respectively. The AFM measurement shows an atomically flat surface with a root mean square roughness of 0.149 nm and a step-flow growth mode. The transmittance spectrum presents a sharp absorption band gap at wavelength 203 nm.