Raman scattering characterization of group III-nitride epitaxial layers including cubic phase

Raman scattering characterizations for two types of group III-nitride epitaxial layers are presented. First, GaN layers where cubic and hexagonal phases are mixed have been studied by Raman microprobe. It is shown that the dominant phase can be estimated by the observation of the transverse-optic (TO) phonon band spectra. Planar distributions of the phase-mixing ratio are examined by a two-dimensional analysis. Second, cubic Al x Ga 1− x N mixed crystals have been studied. With the increase of AlN molar fraction x , the TO phonon shows up-shift in the frequency. However, the shifts are much smaller than those expected from the linear interpolation, which may suggest a two-mode behavior for the TO mode of mixed crystals.