Strain and composition dependence of the E-1(TO) mode in hexagonal Al1-xInxN thin films

Infrared spectroscopic ellipsometry is used to study the influence of strai n and composition on the transverse-optical phonon mode of E-1 symmetry in hexagonal Al1-xInxN films for 0.12 less than or equal tox less than or equa l to0.21. The 0.1-0.2-mum thick films were grown on slightly compressively strained hexagonal GaN buffer layers, or directly on [0001] sapphire by met alorganic vapor phase epitaxy. The Al1-xInxN E-1(TO) phonon shows a one-mod e behavior in contrast to recent theoretical predictions [H. Grille, C. Sch nittler, and F. Bechstedt, Phys. Rev. B 61, 6091 (2000)]. Films grown on Ga N reveal the influence of strain on the phonon mode frequencies due to pseu domorphic film growth. Al1-xInxN deposited directly on sapphire possesses p honon modes which indicate fully relaxed film growth. (C) 2001 American Ins titute of Physics.