Precipitates in AlGaN epilayers grown by metallorganic vapor phase epitaxy

The precipitates were investigated in undoped AlGaN epilayers grown by metal organic vapor phase epitaxy. Surface morphologies above the precipitates studied via atomic force microscopy are characterized by tiny protuberances. The precipitates were detected to contain C impurities by a scanning electron microscope with energy dispersive X-ray spectroscopy. In bright-field transmission electron microscope images, the precipitate appeared as a dark contrast region surrounded by a number of punched out dislocations, differing from that of nanopipes. The difference in the images suggests that the precipitates in the present samples have a different structure due to a different formation mechanism. (C) 2002 Elsevier Science B.V. All rights reserved.