Boron as an anti-surfactant in sublimation growth of AlN single crystals

We study the influence of B evaporating from BN crucible walls on the nucleation and growth of AlN by a physical vapor transport. An experimental analysis by means of electron microscopy and optical spectroscopy shows that B incorporation and surface segregation depends on the orientation of the respective surface facet. Surface segregation is found to be predominant on {11-20} facets. This leads to the formation of wurtzite BN nuclei on these facets which extend over the whole surface and may form closed layers. Both boron surface segregation and growth of BN nuclei influence Al and N adsorption and surface diffusion, and in consequence reduce the growth rate. The differences in surface segregation of B on different facets can be understood in terms of incorporation kinetics of boron adatoms into the AlN crystal. B thus acts as a facet selective antisurfactant. (c) 2006 American Institute of Physics.