Raman active E2 modes in aluminum nitride films

The vibrational spectrum of AlN thin films has been studied in recent years by theoretical and experimental methods, but there is still a lack of full knowledge of the Raman shift of the active E₂ modes of this material. Early work by Carlone et al. 1] has indicated that the E₂ modes of AlN deposited on Si occur at frequencies of 303cm^-1 and 426cm^-1. In the present study, Raman spectra of AlN deposited by magnetron sputtering on polished Si, quartz and BK7 substrates and also the Raman spectrum of pure Si, were compared to show that these peaks can actually be assigned as Raman peaks of Si, instead of AlN Raman peaks. We show that the Raman lines at 240cm^-1 and 650cm^-1 are the true AlN E₂ Raman peaks in agreement with calculated and experimental works reported in the literature that indicate the occurrence of the low and high E₂ Raman modes of AlN in the ranges (228-252)cm^-1 and (631-665)cm^-1, respectively.