Correlation among Growth Conditions, Morphology, and Optical Properties of Nanocolumnar InGaN/GaN Heterostructures Selectively Grown by Molecular Beam Epitaxy

This work reports on the selective area growth mechanism of green-emitting InGaN/GaN nanocolumns with long InGaN sections (330–410 nm) grown by molecular beam epitaxy on GaN/sapphire. The evolution of the morphology of the InGaN segment is found to depend critically on the nominal III/V ratio as well as the diameter of the GaN section, both affecting the local III/V ratio at the top of the nanocolumn. Depending on the local III/V ratio, either metal or nitrogen rich, the diameter of the InGaN segment increases or decreases, respectively, compared to the initial diameter of the GaN segment. In addition, the In distribution inside the InGaN segment is found to depend on the local III/V and In/Ga ratios, i.e., increasing In content toward the top under local metal rich conditions and decreasing In content toward the top under locally N rich conditions.