Origin of green coloration in AlN crystals grown on SiC seeds

The origns leading to the appearance of a green color of AlN crystals grown by sublimation on SiC seeds are investigated. It was shown by the method of secondary ion mass spectroscopy that the color of crystals weakly depends on the content of silicon and carbon, and a green or dark color appears only with an increased content of carbon in comparison with silicon. The presence of a separate amorphous carbon phase in these crystals was established by the method of Raman light scattering. The separation of the carbon phase in the process of crystal growth makes it difficult to obtain high-quality AlN crystals, as well as AlN-SiC solid solutions. The influence of growth conditions on the optical properties of AlN crystals is analyzed.