ISSN 2320-5407 International Journal of Advanced Research (2016), Volume 4, Issue 2, 286-293 286 Journal homepage: http://www.journalijar.com INTERNATIONAL JOURNAL OF ADVANCED RESEARCH RESEARCH ARTICLE TEMPERATURE AND POLARISATION DEPENDENT REFLECTIVITY OF THE C FREE EXCITON OF A-PLANE ORIENTED ZNO EPILAYERS GROWN BY PLASMA-ASSISTED MOLECULAR BEAM EPITAXY. Alioune. A. DIOUF, Bassirou. LO, Moustapha. BA, Mouhamed. B. GAYE, Ibrahima. NIANG, Mamadou. MBAYE, Pape. M. WADE and Aboubaker.C. Beye. Groupe Physique des Solides et Sciences des Matériaux, Faculté des Sciences et Techniques, Université Cheikh Anta Diop de Dakar (UCAD), B.P. 25114, Dakar-Fann Dakar, Sénégal. Manuscript Info Abstract Manuscript History: Received: 15 December 2016 Final Accepted: 19 January 2016 Published Online: February 2016 Key words: Excitonic; Photoluminescence; reflectivity; MBE; a- plane ZnO; thin film. *Corresponding Author Alioune. A. DIOUF. The photoluminescence (PL) and reflectivity (Ref) properties of a-plane oriented ZnO epilayers, grown by molecular beam epitaxy (MBE) on r- plane oriented sapphire substrate, have been investigated. At low temperature donor-bound exciton (DX) emission (3.355-3.383eV) and the C free excitonic transitions (3.427-3.436eV) were identified through polarization dependent photoluminescence and reflectivity measurements. The DX plays a major role in PL spectra at low temperature, while the free exciton transition (FX) gradually dominates the spectrum with increasing temperatures. In the π polarisation, first the temperature-dependent variations of the PL spectra and of the integrated intensity of the C-free exciton were studied. The activation energy of the C-free exciton was calculated to be 59 meV from the temperature dependent quenching of the integral intensities. Then, the temperature dependence of the reflectivity peak energy position of the C-free exciton, was plotted and fitted. Our results substantiated the excitonic nature of the PL emission of the a-plane ZnO thin film, in the  polarisation (E∥c) axis. Copy Right, IJAR, 2016,. All rights reserved. Introduction:- Zinc oxide (ZnO) is a versatile functional material. Its direct wide band gap (3.37 eV) at room temperature and high exciton binding energy (60 meV) had lead to extensive research on ZnO (John Wiley et al., 2011; Ümit Özgur et al., 2010). In the UV region laser devices operating at room temperature (C. Y. Liu et al., 2014) have been studied. Several studies of bulk ZnO were published in the literature (Robert Triboulet, 2014; C. Klingshirn, 2007) and layers were obtained by different growth method (S.H. Parka et al., 2007; Kyung Ho Kim et al., 20014). Since the presence of an internal electric field parallel with the c-axis in the wurtzite structures, has been confirmed experimentally in ZnO/MgZnO quantum well structures (J.-M. Chauveau et al., 2013), growth of quantum wells ZnO has attracted much more people (J. M. Chauveau et al., 2013; G. Tabares et al., 2015). In fact this inherent internal electric field acts to reduce the binding energy of the free excitons in ZnO-based quantum well structures which is detrimental to the performance of room temperature devices based in such a system. In a-plan ZnO-based quantum well structures, the c-axis of the substrate is in the plane of the ZnO epilayer and thus is perpendicular to the direction of confinement in the quantum wells. In other words the induced electric fields will have no effect on the exciton binding energy in the quantum wells. Recently, the transport of indirect excitons in ZnO quantum wells (G. Tabares et al., 2015; Y.Y. Kuznetsova et al., 2015) and the light polarization sensitive photodetectors as a function of the substrate as studied with m and r-plane homoepitaxial ZnO/ZnMgO quantum wells. However though the principal challenge for realizing ZnO optoelectronic devices is the lack of high-conductivity p-type ZnO, a good understanding of the properties of the material is essential for tailoring the material for specific applications and for developing the devices. Photoluminescence (PL) analysis is a very conventional and effective tool for characterizing