Orientation of the nanocrystallites in AlN thin film determined by FTIR spectroscopy

Abstract

Aluminum Nitride (AlN) films were deposited at 450°C in nitrogen ambient at a pressure of 0.1 Pa and at a laser incident fluence of ∼3 J/cm2 and pulse repetition rate of 40 Hz. Grazing Incidence X-ray Diffraction patterns evidenced the presence of nanocrystallites in the amorphous AlN matrix. In the FTIR spectra the characteristic Reststrahlen band of AlN crystal with a hexagonal lattice is observed but it is quite broadened (950-550 cm-1). The angular dependence of the reflectance spectra in p-polarised incidence radiation demonstrates the sensitivity of the A1LO phonon mode of the AlN nanocrystallites to their orientation toward the normal to the substrate surface. With decrease of the incidence beam angle the intensity of the A1LO phonon mode diminishes and softening of the resonance frequency occurs.