On the mixed nature of the 740 cm−1 band in wurtzite GaN films: A polarized Raman scattering investigation

A detailed study of the polarized Raman scattering of wurtzite GaN films is presented, focusing on the nature of the band centered at 740 cm−1 observed in the X(Z, Z)X configuration. The origin of this band is ascribed to the mixed contribution of the A1 and E1 longitudinal phonon modes coupled with the free carrier excitation. The spectral profile of the 740 cm−1 Raman band has been successfully reconstructed through a linear combination of the A1-E1 longitudinal phonon plasmon-coupled modes, leading to a free carrier concentration in good agreement with Hall effect measurements.