IR-reflectance assessment of the tilt angle of AlN-wurtzite films for shear mode resonators

In this paper we propose the use of infrared spectroscopy as an alternative technique to X-ray diffraction for the assessment of the crystal orientation of aluminum nitride thin films. Infrared scans of samples with different tilt angles of the c-axis are measured to accurately determine the structure of the longitudinal optical absorption band, which is found to be the composition of the contributions of three different populations of grains with different angles of tilt of the c-axis. A direct relationship is established between the wavenumber of these contributions and the actual angle of tilt measured through a XRD ψ-scan.