Red-Emitting InGaN-Based Nanocolumn Light-Emitting Diodes with Highly Directional Beam Profiles

摘要

Various InGaN/GaN pn-junction nanocolumn arrays arranged in a triangle lattice are grown on the same substrate while changing the nanocolumn diameters (D_(n-GaN)) of the underlying n-side GaN region under the lattice constant (L) of 340 nm. The nanocolumn diameter increases during the growth of the active InGaN and p-side GaN regions. The periodic arrangement of nanocolumns leads to a photonic crystal effect. Redshift of the band edge wavelength, from 573 to 629 nm, is observed as D_(n-GaN) increases from 159 to 282 nm. This phenomenon can be explained by the fact that the larger filling factor increases the effective refractive index of the nanocolumn system, resulting in a redshift of the band edge. The light diffraction at the photonic band edge induces the directional radiation beam from the surface of the nanocolumn system. Using the nanocolumn array with D_(n-GaN) = 260 nm, the red-emitting (λ = 637 nm) nanocolumn light-emitting diodes with the radiation angle of ±30° are demonstrated.