"Vibrational and optical properties of AlN grown on Si(111)"

We present optical measurements of hexagonal AlN grown by gas-source molecular beam epitaxy on (111)-oriented silicon wafers. Fourier-transform infrared (FTIR) reflectance and absorption measurements are used to determine the E/sub 1/- and A/sub 1/-symmetry vibrational energies in AlN (TO and LO). FTIR reflectance data are modeled using a non-isotropic dielectric function. The phonon energies are also measured by Raman scattering, which includes the E/sub 2/-symmetry phonons, as well as A/sub 1/(TO), A/sub 1/(LO), and E/sub 1/(TO). Ellipsometry measurements between 0.73 and 6.60 eV allow us to determine the optical constants. The energy gap is found to lie between 6.1 and 6.2 eV.