Three-dimensional GaN dodecagonal ring structures for highly efficient phosphor-free warm white light-emitting diodes

Abstract

Warm and natural white light (i.e., with a correlated colour temperature <5000 K) with good colour rendition (i.e., a colour rendering index >75) is in demand as an indoor lighting source of comfortable interior lighting and mood lighting. However, for warm white light, phosphor-converted white light-emitting diodes (WLEDs) require a red phosphor instead of a commercial yellow phosphor (YAG:Ce), and suffer from limitations such as unavoidable energy conversion losses, degraded phosphors and high manufacturing costs. Phosphor-free WLEDs based on three-dimensional (3D) indium gallium nitride (InGaN)/gallium nitride (GaN) structures are promising alternatives. Here, we propose a new concept for highly efficient phosphor-free warm WLEDs using 3D core-shell InGaN/GaN dodecagonal ring structures, fabricated by selective area growth and the KOH wet etching method. Electrically driven, phosphor-free warm WLEDs were successfully demonstrated with a low correlated colour temperature (4500 K) and high colour rendering index (R = 81). From our findings, we believe that WLEDs based on dodecagonal ring structures become a platform enabling a high-efficiency warm white light-emitting source without the use of phosphors.

A discrete core-shell-like micro-light-emitting diode array grown on sapphire nano-membranes

“…Emissions with shorter wavelengths were measured from the facets in order of {1122}, {1101}, and (0001), in good agreement with the results in the literature [42][43][44][45] . The emissions with various wavelengths were attributed to the differences in growth rates and indium incorporation on each facet 45,46 . In addition, the thinner InGaN quantum well in semi-polar facets reduced the QCSE and leads www.nature.com/scientificreports www.nature.com/scientificreports/ to an increased emission energy, which is consistent with the CL results.…”

Surface/Interface Engineering for Constructing Advanced Nanostructured Light-Emitting Diodes with Improved Performance: A Brief Review

“…Due to the large surface-to-volume ratios of the 1D nanomaterials, the surface plays a key role in the optical properties of 1D nanometer material LEDs [80][81][82][83][84][85][86][87][88][89][90]. Due to the existence of surface states, a Fermi-level pinning effect will occur, and the resulting transverse electric field effect and related surface non-radiative recombination will be very unfavorable to one-dimensional nanostructured-led devices [80][81][82].…”

“…The results show that the GaN-based nanowires LED can realize relatively high internal quantum efficiency from the deep green to red wavelength range. In 2018, Sim et al designed highly efficient white LEDs using the 3D InGaN/GaN structure [87]. It can be proved by the experimental results that white LEDs based on dodecagonal ring structures are a platform enabling a high-efficiency warm white light-emitting source.…”

Development of Monolithically Grown Coaxial GaInN/GaN Multiple Quantum Shell Nanowires by MOCVD

“…Many attempts to fabricate phosphor-free white light LEDs using selectively grown GaInN/GaN nanostructures have been reported [25][26][27]. Coaxial GaInN/GaN dodecagonal ring structures have achieved white LEDs with a low CCT (4500 K) and high CRI (81), but their effectiveness depends on the thicknesses of GaInN/GaN layer and the In contents at multiple facets [28]. Yellow-white emission was reported from composition-graded GaInN/GaN nanocolumns that were sequentially grown at 700 • C, 675 • C and 650 • C via plasma-assisted molecular beam epitaxy [27].…”