Faceting in AlN bulk crystal growth and its impact on optical properties of the crystals



The surface of bulk AlN single crystals grown by PVT on Al-polar (0001) seeds is typically constructed from prismatic, pyramidal, and basal plane facets. Simultaneous growth on different facets with different surface kinetics leads to formation of a zonar structure which is visible due to local differences in coloration in the wafers. Four zones on an AlN wafer representing (1) growth on {1013} pyramidal facets, (2) growth adjacent to ridges and (0001) basal plane facets, and (3) + (4) outer and centre areas corresponding to surface depressions are investigated. They show striking differences in optical absorption (OA) spectra, cathodoluminescence (CL) spectra and chemical analysis (SIMS). In areas near ridges and (0001) facets and in centres of depressions, deep-UV absorption as well as luminescence is significantly increased. We assign OA and CL bands observed in these zones to the presence of carbon and/or the lack of oxygen due to local segregation effects caused by faceting. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)