International Scholarly Research Network ISRN Condensed Matter Physics Volume 2012, Article ID 184023, 6 pages doi:10.5402/2012/184023 Research Article A Comparative Study of Dislocations in HVPE GaN Layers by High-Resolution X-Ray Diffraction and Selective Wet Etching Vladimir Ivantsov and Anna Volkova GaN Lab, Ostendo Technologies, Inc., 12214 Plum Orchard Drive, Silver Spring, MD 20783, USA Correspondence should be addressed to Vladimir Ivantsov, vladimir.ivantsov@ostendo.com Received 18 June 2012; Accepted 31 July 2012 Academic Editors: A. Oyamada, M.-H. Phan, and H.-D. Yang Copyright © 2012 V. Ivantsov and A. Volkova. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. It has been shown during the present study that the E-etching at elevated temperatures can be adopted for the dislocation etching in hydride vapor-phase epitaxy (HVPE) GaN layers. It has been found that the X-ray diffraction (XRD) evaluation of the dislocation density in the thicker than 6 μm epilayers using conventional Williamson-Hall plots and Dunn-Koch equation is in an excellent agreement with the results of the elevated-temperature E-etching. The dislocation distribution measured for 2-inch GaN-on- sapphire substrate suggests strongly the influence of the inelastic thermal stresses on the formation of the final dislocation pattern in the epilayer. 1. Introduction It is the optoelectronic properties that make GaN extremely attractive for a wide range of applications. It is needless to say that such defects as dislocations can adversely influence them. The high-resolution XRD is able to provide mea- surements of the dislocation densities in a nondestructive way. Therefore the XRD can be considered as the preferred metrology technique for monitoring of product substrates. Despite a number of the XRD methods developed for evaluation of the dislocation density [1], they are far from having reached conclusive results from a metrological point of view. Recently developed selective wet etching of the dislocations in bulk GaN has been confirmed to show the strict correspondence between the etch pits density (EPD) and the dislocation density measured by transmission electron microscopy (TEM) [2]. The purpose of this study is to examine the relationship between the etch pit density after selective wet etching and the dislocations density measured by the XRD in mosaic crystal approximation for the HVPE GaN epilayers grown on sapphire substrates. 2. Selective Wet Etching Experiments Among various etching techniques aiming to be used for dislocation counting in GaN, the selective wet etching with a molten eutectic flux of KOH and NaOH (dubbed E-etchant) has the most prominent foundation to be considered as the most appropriate. This technique has been adopted for the etching part of the present study. Both intentional introduction of dislocations by indentation and TEM mea- surements confirmed direct correspondence of the etch pits to dislocations in bulk GaN [3, 4]. Application of the E- etching to the epitaxial GaN has been found to show that the edge dislocations could be missed on etching pattern [3]. It was suggested in [5] that the major factor influencing etching result could be the etching temperature and this temperature has required careful consideration and research. Whole 2-inch diameter GaN-on-sapphire substrates as well as their parts have been used as samples for the study. The thicknesses of the HVPE epilayers ranged from 5 to 21 μm. Both undoped and Mg- or Si-doped samples have been tested. The samples were wiped clean with distilled water and acetone and placed face-up in a platinum wire