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

We report the observation of ultraviolet and visible near-resonance enhance d Raman scattering in epitaxial wurtzite Al1-xInxN (0001) (0 less than or e qual tox <0.7) thin films. The films (thickness similar to 150 nm) were gro wn 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 ex citation energy. On the other hand, samples with x similar to0.6 (energy ba nd gap similar to2.5 eV) show significant enhancement with 514.5 nm (2.41 e V) excitation. The A(1)(LO) and E-2 zone center phonons have been observed for all the samples. The A(1)(LO) phonon frequency shows the expected decre ase with increasing x. The E-2 mode shows a two-mode behavior supporting th e recent theoretical predictions. Due to increased resonance enhancement, s trong second- and third-order spectra are seen in some films. (C) 2001 Amer ican Institute of Physics.