Plan-view transmission electron microscopy study on coalescence overgrowth of GaN nano-columns by MOCVD

Abstract

We report the nanostructure study results, mainly based on plan-view transmission electron microscopy (TEM) on the coalescence process during the overgrowth by metalorganic chemical vapor deposition of GaN nanocolumns grown by molecular beam epitaxy. In cross-section scanning electron microscopy images, one can observe a two-stage coalescence overgrowth process. First, a group of nearby nanocolumns is merged into a thicker column. One of the possible merging processes is the growth of a bridging domain between two columns for their connection. The thicker columns are then developed into horn-shaped structures for the second-stage coalescence. Because different columns may have different crystal orientations, stacking faults can be formed for implementing the coalescence between two domains. Such stacking faults around the boundaries of merged domains represent one of the major kinds of defect after the threading dislocation density is reduced based on the nanocolumn growth technique.