A new preparation approach for high-resolution TEM analysis of electrically active defects in p-GaN HEMT devices from two orthogonal perspectives

The characterization of crystal defects inside GaN epi layers, especially dislocations, is of major interest to further improve the performance and reliability of GaN high-electron-mobility transistor (HEMT) devices. This work presents a new approach for correlative electroluminescence (EL) defect localization and 3D transmission electron microscopy (TEM) analysis to determine and quantify related structural defects with nm dimensions. New focused ion beam (FIB) preparation workflows allowing a combined cross-sectional and planar TEM analysis of localized defect sites will be introduced. It will be demonstrated that nm-sized defects and the structure of critical dislocations within the relatively large EL spot area can be identified and quantified. The workflow is exemplarily applied to stressed normally-off p-GaN HEMT devices. The three-dimensional route of a dislocation bunch in relation to the HEMT gate structure is investigated, and the dislocation core structure is visualized by atomically resolved TEM imaging.