Investigation of the growth characteristics of epitaxial GaN layers on sapphire by microcathodoluminescence

A study was made of the growth regimes of undoped epitaxial GaN layers unde r various substrate nitriding conditions. It was observed that at a nitridi ng temperature of similar to 1000 degrees C films are formed with typical g rowth characteristics in the form of hexagonal pyramids separated by a smoo thed surface. The cathodoluminescence pattern in the pyramids revealed a fi ne structure in which a region of donor-acceptor recombination could be ide ntified. The formation of acceptor levels in this region was attributed to intrinsic structural defects in the GaN layers with unsaturated (broken) bo nds. The presence of a donor-acceptor recombination line in mirror-smooth e pitaxial films may indicate that these films contain this type of structura l defect. (C) 1999 American Institute of Physics. [S1063-7850(99)00204-9].