Materials Science and Engineering B 165 (2009) 153–155 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Surface and interface-related phonon modes in InN/AlN nanolayer structures E. Valcheva a,∗ , M. Baleva a , G. Zlateva b a Faculty of Physics, Sofia University, 5 J. Bourchier blvd, 1164 Sofia, Bulgaria b Faculty of Medicine, Sofia University, 1 Koziak str, 1407 Sofia, Bulgaria article info Article history: Received 25 August 2008 Received in revised form 9 September 2009 Accepted 11 September 2009 Keywords: Nitrides InN Interface phonon-polariton dispersion Raman scattering abstract We study the conditions for appearance and observation of surface and interface phonon-polariton (SPP and IPP) modes in thin InN layers grown on sapphire using AlN buffer. Theoretical dispersion relations of the IPP modes in the system air/InN/AlN/sapphire for different thickness of the InN layer are obtained. Features, additional to those due to the compounds optical phonons, are observed. The asymmetry in the experimentally observed Raman mode peaks is associated with the appearance of interface phonon- polariton excitations at wave-numbers between the TO and LO modes, which are not reported by now. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The reduced dimensionality in multilayer structures gives rise to vibrational modes that are fundamentally different from the bulk ones—these are the interface phonon-polariton modes. They often become dominant in nanoscaled structures which imposes an increased interest in this subject. The interface phonon modes are expected to appear between the longitudinal (LO) and transverse optical (TO) frequencies of the media, where the dielectric function is negative. Considerable attention has been paid to the localized interface phonon-polariton modes in superlattice (SL) and multiquantum well structures from III–V compounds, e.g. AlAs–GaAs SLs [1]. There are also studies on the III-nitride material system, mostly on AlN/GaN [2–4], while the problem completely lacks investigation in structures comprising InN. InN is still the least investigated representative of the group III-nitrides, although it experienced a renaissance with the devel- opment of sophisticated epitaxial growth techniques as molecular beam epitaxy (MBE) and metal-organic chemical vapour deposi- tion (MOCVD). The remarkable electrical and optical properties such as small effective mass, high electron drift velocity and small band-gap energy (∼0.7 eV) make InN a promising material for high-frequency transistors, telecommunication-wavelength ∗ Corresponding author. Tel.: +359 2 8161 898; fax: +359 2 9625 276. E-mail address: epv@phys.uni-sofia.bg (E. Valcheva). optoelectronic devices, and solar cells. The interest in inter- face polariton modes stems from the knowledge that modes localized at the interfaces of multilayer heterostructures are found to play an important role in the electron–phonon interactions and hence to the operation of optoelectronic devices. In this work we study in particular the conditions for appear- ance and observation of surface and interface phonon-polariton (SPP and IPP) modes in thin InN layers grown on sapphire using AlN buffer. Theoretical dispersion relations of the IPP modes in the sys- tem air/InN/AlN/sapphire for two different thicknesses of the InN layer are obtained. The asymmetry in the experimentally observed Raman mode peaks was associated with the appearance of inter- face phonon-polariton excitations at wave-numbers between the TO and LO modes. 2. Dispersion relations of surface and interface phonon-polaritons The dispersion relations can be derived within the dielectric continuum model. The existence of interfaces in a multilayer structure is then reflected by periodic modulation of the dielec- tric function. Further phonon dispersion relations are calculated from the Maxwell equations following the approach of Mills and Maradudin [5]. As far as more complicated four-layer structure air/InN/AlN/sapphire is considered a system of equations for the four interfaces was constructed. In the assumption of isotropic media and light velocity c →∞, and applying conventional bound- ary conditions for continuity of the polariton electric field at each 0921-5107/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2009.09.016