Low-temperature α-alumina thin film growth: ab initio studies of Al adatom surface migration

Investigations of activation energy barriers for Al surface hopping on alpha-Al2O3 (0 0 0 1) surfaces have been carried out by means of first-principles density functional theory calculations and the nudged elastic band method. Results show that surface diffusion on the (most stable) Al-terminated surface is relatively fast with an energy barrier of 0.75 eV, whereas Al hopping on the O-terminated surface is slower, with barriers for jumps from the two metastable positions existing on this surface to the stable site of 0.31 and 0.99 eV. Based on this study and on the literature, the governing mechanisms during low-temperature alpha-alumina thin film growth are summarized and discussed. Our results support suggestions made in some previous experimental studies, pointing out that limited surface diffusivity is not the main obstacle for alpha-alumina growth at low-to-moderate temperatures, and that other effects should primarily be considered when designing novel processes for low-temperature alpha-alumina deposition.