Structural and optical properties of disc-in-wire InGaN/GaN LEDs.

This study examines the role of the microstructure and optical properties of InGaN/GaN nanowire LED structures on Si(111) having different nanowire coverages. Cathodoluminescence (CL) measurements show that all samples exhibit broad emission around the intended energy, 1.95 eV (635 nm). While the absolute emission intensity is hard to compare for CL measurement, the bandgap emission (∼3.4 eV) coming from the GaN root is more pronounced as coverage of nanowires decreases, which has less coalescence formation. The width of the emission peak is likely due to variations in the morphology of the InGaN discs within the wires, as faceted layers with different thicknesses and quantum dots are observed by transmission electron microscopy. Nonepitaxial six-fold symmetric lateral branching, called "nanocrowns," emanate from stacking faults within the active regions. These features likely reduce optical emission as a result of grain boundaries between the nanocrown and nanowire.