Comparison of Luminescence and Physical Morphologies of GaN Epilayers
Carol Trager-Cowan , P. G. Middleton, K. P. O'Donnell
Department of Physics and Applied Physics, University of Strathclyde
S. Ruffenach-Clur, Olivier Briot
Groupe d'Etude des Semiconducteurs, GES-CNRS
This article was received on Tuesday, June 17, 1997 and
accepted on Monday, September 15, 1997. 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
and 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
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directions, displays some interesting acceptor related luminescence.