Ultraviolet and visible resonance-enhanced Raman scattering in epitaxial Al1−xInxN thin films

We report the observation of ultraviolet and visible near-resonance enhanced Raman scattering in epitaxial wurtzite Al1−xInxN (0001) (0⩽x<0.7) thin films. The films (thickness∼150 nm) were grown by plasma source molecular beam epitaxy on sapphire (0001) substrates. A substantial spectral enhancement is seen for Al-rich samples using 244 nm (5.01 eV) radiation due to the closeness of their band gap energy to the excitation energy. On the other hand, samples with x∼0.6 (energy band gap ∼2.5 eV) show significant enhancement with 514.5 nm (2.41 eV) excitation. The A1(LO) and E2 zone center phonons have been observed for all the samples. The A1(LO) phonon frequency shows the expected decrease with increasing x. The E2 mode shows a two-mode behavior supporting the recent theoretical predictions. Due to increased resonance enhancement, strong second- and third-order spectra are seen in some films.