We study the vibrational spectrum of AlN grown on Si(111). The AlN was deposited using gas-source molecular beam epitaxy. Raman backscattering along the growth c axis and from a cleaved surface perpendicular to the wurtzite c direction allows us to determine the E21, E22, A1(TO), A1(LO) and E1(TO) phonon energies. For a 0.8-μm-thick AlN layer under a biaxial tensile stress of 0.6 GPa, these are 249.0, 653.6, 607.3, 884.5, and 666.5 cmࢤ1, respectively. By combining the Raman and x-ray diffraction studies, the Raman stress factor of AlN is found to be −6.3 ° 1.4cm−1/GPa for the E22 phonon. This factor depends on published values of the elastic constants of AlN, as discussed in the text. The zero-stress E22 energy is determined to be 657.4 ° 0.2cmࢤ1. Fourier-transform infrared reflectance and absorption techniques allow us to measure the E1(TO) and A1(LO) phonon energies. The film thickness (from 0.06 to 1.0 μm) results in great differences in the reflectance spectra, which are well described by a model using damped Lorentzian oscillators taking into account the crystal anisotropy and the film thickness.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 2001|