Affiliation: | a University of Strathclyde, Department of Physics and Applied Physics, John Anderson Building, 107 Rottenrow, Glasgow G4 0NG, UK b Centre National de la Recherche Scientifique, Groupe d'Etude des Semiconducteurs, Université de Montpelier II, Place Eugène Bataillon, Case courrier 074, 34095 Montpellier, Cedex 5, France |
Abstract: | In this paper we examine a series of four GaN epilayers grown by MOVPE on sapphire substrates with different AlN buffer layer thicknesses. We examine the effect of the buffer layer thickness on the physical and optical properties of the samples via optical microscopy, cathodoluminescence imaging, photoluminescence, and cathodoluminescence spectroscopy. While the morphological and optical properties of all the films (excepting that with the thinnest buffer layer of 30 nm) are good, i.e. the films are smooth and the luminescence is dominated by excitonic luminescence, a number of circular island like features are observed in all the films whose density decrease with increasing buffer layer thickness. A large circular island present on the sample with the thinnest buffer layer and surrounded by cracks in the 110 directions, displays some interesting acceptor related luminescence. |