Vibrational and electrical properties of hexagonal La_2O_3 films

摘要

La_2O_3 films are obtained by annealing in vacuum La(OH)_3 layers produced upon air exposure of La_2O_3 layers grown using atomic layer deposition. Sample thickness determines whether hexagonal or cubic La_2O_3 form. The observed infrared active phonon mode with minimum frequency for hexagonal La_2O_3 films is located at 198 cm~(-1), in good agreement with the first principles calculations, and at a lower frequency than the corresponding mode for cubic La_2O_3 is at 235 cm~(-1). Accordingly, electrical measurements reveal a dielectric constant around 27 for hexagonal La_2O_3 films, significantly higher than the one around 17 derived for cubic La_2O_3 layers.