Orientation-dependent properties of aluminum nitride single crystals

We have measured the optical properties of different facets and different growth zones in AlN bulk single crystals grown by physical vapor transport. These crystals have a pronounced zonal structure. The systematic investigation shows that absorption and luminescence properties are similar to AlN crystals and epitaxial layers grown with other techniques. However, the intensity and position of below band‐gap features was found to vary strongly with the zone or facet investigated. We conclude that intrinsic defect formation and impurity concentration strongly depend on the growth direction. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)