In the present work, the effect of surface morphology of nanotextured InAs/Ge (1 1 1) epilayers on their optical properties is presented. Spectroscopic ellipsometry measurement of dielectric constants using effective medium approximation reveals that nanotextured InAs layers have reduced value of dielectric constant compared to the bulk in the energy range of 1.6-6 eV, which is attributed to its morphology and quantum confinement effect. The anisotropy in the shape of the InAs nanostructures also gives rise to anisotropic dielectric constant leading to partial relaxation in polarization dependent Raman selection rule. A phonon mode observed at similar to 234 cm(-1) in the InAs/Ge heterostructure is identified as plasmon-LO phonon coupled mode originating from the accumulated surface of InAs and this is found to be independent of the morphology of InAs structures. This identification is also corroborated with the temperature dependent phonon frequency shift of the coupled mode. Carrier concentration of 5-8 x 10(17) cm(-3) for the surface accumulation layer is estimated with the help of the frequency of the coupled mode. (C) 2016 Elsevier B.V. All rights reserved.