Superlattices and Microstructures 40 (2006) 612–618 www.elsevier.com/locate/superlattices Determination of strain and composition in SiC/Si and AlN/Si heterostructures by FTIR-ellipsometry J. Pezoldt a,∗ , Ch. Zgheib b , V. Lebedev a , P. Masri c , O. Ambacher a a FG Nanotechnology, Center of Micro- and Nanotechnologies, TU Ilmenau, PF 100565, 98684 Ilmenau, Germany b Department of Sciences, Notre Dame University, P.O. Box 72, zouk Mikayel, Lebanon c Groupe d’Etude des Semi-conducteurs, Universit´ e de Montpellier II, cc 074, 34095 Montpellier, France Received 5 May 2006; received in revised form 28 July 2006; accepted 31 July 2006 Available online 18 September 2006 Abstract Heteroepitaxially grown 3C-SiC and 2H-AlN layers on Ge modified Si(111) substrates were investigated by Fourier transform infrared spectroscopic ellipsometry. The obtained phonon frequencies increase with increasing Ge pre-deposition indicating a decrease of the residual stress in both wide band gap materials. Additionally, it is shown that infrared ellipsometry allows the analysis of the polytype content of the grown epitaxial layers. c  2006 Elsevier Ltd. All rights reserved. Keywords: Infrared ellipsometry; Heteroepitaxy; Polytypism; Strain 1. Introduction The residual strain and defect density are crucial in mismatched heteroepitaxial structures impacting the properties and the reliability of micro- and optoelectronic devices. Especially, strain control allows to alter and to tune the electronic and optical properties of the formed heterostructures (see for example [1–3]). Depending on the growth conditions and the thickness of the epitaxial layers, they can be either elastically strained due to pseudomorphic growth, or the strain can be relieved by plastic relaxation of the epilayer due to the formation and propagation of dislocations resulting in ∗ Corresponding author. Tel.: +49 3677 693412; fax: +49 3677 693356. E-mail address: joerg.pezoldt@tu-ilmenau.de (J. Pezoldt). 0749-6036/$ - see front matter c  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.spmi.2006.07.030