COMPARISON OF LUMINESCENCE AND PHYSICAL MORPHOLOGIES OF GAN EPILAYERS

In this paper we examine a series of four GaN epilayers grown by MOVPE on sapphire substrates with different AlN buffer layer thicknesses. W e examine the effect of the buffer layer thickness on the physical and optical properties of the samples via optical microscopy, cathodolumi nescence imaging, photoluminescence, and cathodoluminescence spectrosc opy. 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 l uminescence, a number of circular island like features are observed in all the films whose density decrease with increasing buffer layer thi ckness. A large circular island present on the sample with the thinnes t buffer layer and surrounded by cracks in the [11 (2) over bar 0] dir ections, displays some interesting acceptor related luminescence. (C) 1997 Elsevier Science S.A.