Infrared reflection of GaN and AlGaN thin film heterostructures with AlN buffer layers

Infrared reflection spectroscopy is applied to state-of-the-art thin film heterostructures of group-III nitrides on sapphire and Si substrates. The individual layers of GaN and AlGaN and the AIN buffer layer are identified by their phonon frequencies. Under non-perpendicular incidence of the light, A(1)(LO) phonon modes are observed in the wurtzite system. The presence of the very thin AIN buffer layer manifests itself in clear features of the AlN phonons. The A(1)(LO) phonon mode energy is determined in AlxGa1-xN for x approximate to 0.15. Raman spectra confirm our findings. (C) 1996 American Institute of Physics.