Raman scattering and cathodoluminescence characterization of near lattice-matched InxAl1-xN epilayers

We present a Raman scattering and cathodoluminescence study of a set of InxAl1-xN/GaN epilayers with InN fractions around the lattice-matched composition. We observed the A(1)(LO) and InN-like E-2 modes of the alloy, whose frequencies are in good agreement with theoretical predictions, but we were unable to detect the AlN-like E-2 mode. The InN-like E2 mode did not exhibit noticeable frequency shifts in the studied samples. This is explained by the presence of residual strain in the pseudomorphic InxAl1-xN films. A luminescence peak that shifts to lower energies with an increasing InN fraction was observed at energies above the band edge of the GaN substrate. The cathodoluminescence peak energy is lower than expected, indicating a large band-gap bowing in these alloy layers.