Addressing the orientation of defect-related crystal domains by Atom Probe Tomography in III-N heterostructures

Atom Probe Tomography (APT) may be applied as a tool for the assessment of the crystallographic orientation of microstructural features. In the present study, such features are related to defects formed during the growth of AlGaN/AlN quantum dot superlattices. These defects are the origin of the low-energy component of a bimodal luminescence emission in the 230-300 nm spectral range [1]. The defects are cone-shaped, starting at the AlN buffer/superlattice interface and propagating vertically, associated to a dislocation that produces strong shear strain and favors the formation of 30° faceted pits. They also may be responsible for local formation of misoriented domains. We show that the effective surface field intensity maps obtained through the statistics of the charge states <i>n</i> of the field-emitted Al^+<i>n</i> ions can be used as a means to locate the direction of the [0001] crystal pole with respect to the needle axis. This provides a way to track changes of crystal orientations by several degrees and to correlate them with the morphological and chemical features of the sample. The results indicate that such misorientations can occur, but not systematically.<br/>[1] Cañas et al., under review. https://arxiv.org/abs/2310.04201