Superlattices and Microstructures 36 (2004) 573–580 www.elsevier.com/locate/superlattices Infrared ellipsometry and Raman studies of hexagonal InN films: correlation between strain and vibrational properties V. Darakchieva a,∗ , P.P. Paskov a , E. Valcheva a , T. Paskova a , M. Schubert b , C. Bundesmann b , H. Lu c , W.J. Schaff c , B. Monemar a a Department of Physics and Measurement Technology, Linköping University, S-581 83 Linköping, Sweden b Fakultät für Physik and Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany c Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853, United States Abstract The vibrational properties of InN films with different strain have been studied using Infrared ellip- sometry and Raman scattering spectroscopy. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and the strain-free frequencies of the InN E 1 (TO) and E 2 modes. The LO phonons and their coupling to the free-carrier plasmon excitations are also discussed in relation to the carrier concentration in the films. © 2004 Elsevier Ltd. All rights reserved. 1. Introduction The group III nitrides are currently a subject of intense investigations because of the substantial potential for applications for optoelectronic and high-speed devices in the ultra- violet, visible and infrared (IR) energy region. Due to difficulties to fabricate good quality single crystalline epitaxial InN films in the past years the research in the field has been ∗ Corresponding author. Fax: +46 13 142337. E-mail address: vanya@ifm.liu.se (V. Darakchieva). 0749-6036/$ - see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.spmi.2004.09.014