Journal of Crystal Growth 246 (2002) 271–280 Synchrotron white beam topography characterization of physical vapor transport grown AlN and ammonothermal GaN Balaji Raghothamachar a, *,WilliamM.Vetter a , Michael Dudley a ,RafaelDalmau b , Raoul Schlesser b , Zlatko Sitar b , Emily Michaels c , Joseph W. Kolis c a Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275,USA b Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7907, USA c Department of Chemistry, Clemson University, Clemson, SC 29634-0973, USA Abstract Structural defects in AlN single crystals grown by the sublimation method and GaN single crystals grown by the ammonothermal method are characterized by synchrotron white-beam X-ray topography in conjunction with optical microscopy. AlN platelets are either of ð11 % 20Þ or (0001) type depending on the growth conditions. Dislocation densities of the order of 10 3 cm 2 or lower are observed in some crystals. X-ray topographs reveal the presence of growth sector boundaries, inclusions, and growth dislocations that indicate slight impurity contamination. The 2H crystal structure of GaN single crystals obtained by the ammonothermal method was verified by Laue X-ray pattern analysis. GaN crystals grown are of the order of 1mm in size and are either (0001) platelets or [0001] prismatic needles. Generally, prismatic needles are characterized by lower degree of mosaicity than (0001) platelets. r 2002 Published by Elsevier Science B.V. PACS: 61.72.Ff; 81.10.Bk; 81.10.Dn; 81.05.Ea Keywords: A1. Defects; A1. X-ray topography; A2. Growth from vapor; A2. Single crystal growth; B1. Aluminum nitride; B1. Gallium nitride 1. Introduction Wide band gap nitride semiconductors are promising materials for a broad range of electronic and opto-electronic devices. Potential applications include electronic devices capable of operation at elevated temperatures, high power or high fre- quency, and short-wavelength optoelectronic de- vices such as solar blind ultraviolet light detectors, blue light emitting diodes or ultraviolet laser diodes. Currently, some of these applications such as blue LEDs are being realized by growing heteroepitaxial device structures on SiC or sap- phire substrates. However, the severe lattice mismatch as well as chemical incompatibility and *Corresponding author. Tel.: +1-631-632-8501; fax: +1- 631-632-8052. E-mail address: braghoth@ms.cc.sunysb.edu (B. Raghothamachar). 0022-0248/02/$-see front matter r 2002 Published by Elsevier Science B.V. PII:S0022-0248(02)01751-7