Herein, a newly developed birefringence microscope is used to observe dislocations in gallium nitride (GaN) substrates. The comparison results of the observation method using this microscope with other observation methods, such as X‐ray topography and Raman microscopy, confirms that dislocations in a GaN substrate can be detected with a birefringence microscope. In addition, the observation can be carried out as easily as with an optical microscope. It is also found that under certain observation conditions, the direction of the edge component of dislocations can be determined.

The back cover shows a retardation image of c‐plane GaN substrate having dislocation density of 103 cm–2 taken with a birefringence microscope, as presented by Atsushi Tanaka and co‐workers in article number http://doi.wiley.com/10.1002/pssb.201900553. Strain around dislocations appears as contrast in the image. From this contrast, it can be determined to which direction the edge component of the dislocation is oriented. The table below shows the correspondence between the direction of extra half plane of edge component and the contrast. All six equivalent <112¯0> edge components are found in this image.