Vibrational properties of AIN grown on (111)-oriented silicon

We study the vibrational spectrum of AIN grown on Si(111). The AIN 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 AIN layer under a biaxial tensile stress of 0.6 GPa, these are 249.0, 653.6, 607.3, 884.5, and 666.5 cm^-1, respectively. By combining the Raman and x-ray diffraction studies, the Raman stress factor of AIN is found to be -6.3±1.4 cm^-1/GPa for the E₂² phonon. This factor depends on published values of the elastic constants of AIN, as discussed in the text. The zero-stress E₂² energy is determined to be 657.4±0.2 cm^-1. 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.