Identifying threading dislocation types in ammonothermally grown bulk α-GaN by confocal Raman 3-D imaging of volumetric stress distribution

This study demonstrates all-optical Raman scattering study of dislocations in ammonothermally grown α-GaN crystal and identifies an edge a-type threading dislocation (TD) using a confocal Raman 3-D imaging technique. These findings make possible the characterization of volumetric stress field and low TD density distributions over a large area on bulk α-GaN single crystal. The dislocation type effects on Raman shift are also discussed in detail (in order to identify the edge a-type and mixed a+c-type TDs, and theorize the invisibility of the screw c-type TDs). Authors are not aware of any previous reports using the confocal Raman 3-D imaging to identify the edge a-type and mixed a+c-type TDs.