Role of defect centers in recombination processes in GaN monocrystals

A confocal fluorescence microscopic study was carried out on GaN monocrystals grown by molecular beam epitaxy and doped with Mn. The samples were irradiated with mid band gap radiation (488 nm) rather than ultraviolet, and it was found that a strong yellow radiation was emitted by defect centers. Three-dimensional images clearly reveal not only the size and the form of the illuminating defect centers but also their orientations with respect to the plane on which these defects were grown. This is a direct evidence for the radiative recombination at the defect centers when excited by the midgap radiation.