Abstract
The reflectivity and transmission spectra of aluminum nitride have been measured using unpolarized radiation in the wavelength region 2 to 30 μ. The dielectric parameters and the zone-center () opticalmode energies [transverse (TO) and longitudinal (LO)] have been calculated from the reflectivity measurements using dispersion theory. The values obtained are TO=82.7 meV (666.7 ), LO=113.6 meV (916.3 ), , and . From these data the value calculated for the Szigeti effective charge is . Polarization measurements have revealed a sharp minimum in the reststrahlen band for parallel to the axis at ∼111.0 meV. Otherwise the reflectivity curves appear identical for both polarizations. Thirteen absorption bands have been observed on the high-energy side of the reflectivity band. A tentative interpretation is proposed in which these bands are considered to be due to combinations of six representative phonon branches at or near the Brillouin-zone boundary (). The phonon energies resulting from this interpretation are LO=91.4, T=82.5, T=78.1, LA=62.9, T=55.3, and T=50.9 meV.
- Received 14 November 1966
DOI:https://doi.org/10.1103/PhysRev.158.833
©1967 American Physical Society