Using Fourier transform infrared grazing incidence reflectivity to study local vibrational modes in GaN

Abstract

Both Fourier transform infrared (FTIR) grazing incidence reflectivity and FTIR transmission methods have been used to study GaN films grown on $\mathrm{\alpha -}{\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ (0001) substrates by atmospheric pressure metal-organic chemical vapor deposition and low pressure metal-organic chemical vapor deposition. The results show that in the frequency range from 400 to 3500 cm⁻¹ the signal-to-noise ratio of the FTIR grazing incidence measurement is far higher than that of the FTIR transmission measurement. Some new vibrational structures appearing in the former measurement have been discussed. The features around 1460 and 1300 cm⁻¹ are tentatively assigned to scissoring and wagging local vibrational modes of ${\mathrm{CH}}_{\mathrm{2}}$ in GaN, respectively.