Optical spectroscopy of a-plane-oriented ZnO epilayers grown by plasma-assisted molecular beam epitaxy
a-plane ZnO layers were successfully grown, by plasma-assisted molecular beam epitaxy, on r-plane (011–2) sapphire substrates. Several features attributed to the A, B and C free excitonic transitions are identified through temperature-dependent photoluminescence (PL) and reflectivity measurements. The temperature dependence of the peak energy positions of these transitions was studied from 8 K to 300 K. So, the PL peak energy of the A free exciton was plotted and fitted with a Varshni empirical equation. In the ? polarization (E?c), for which A and B are allowed, the reflectivity spectrum measured at 8 K was fitted by using a program based on the theory of the spatial resonance dispersion Hopfield model. Our results indicate that the A and B free excitonic features are at a higher energy than those in ZnO on c-oriented sapphire and show a good PL even at 250 K. These results also show that the new and intense emission peak observed in the region of the first phonon replica (3.33–3.28 eV) and identified as a stacking fault in the epilayer disappears at high temperature above 150 K.
Auteur(s) : B Lo, M B Gaye, A Dioum, C M Mohrain, M S Tall, J M Chauveau, M D Tesseire, S Ndiaye, and A C Beye.
Année de publication : 2013
Revue : Applied Physics A
Type : Article
Statut Editorial : Indexé dans les bases de la spécialité
Mise en ligne par : NDIAYE Sossé