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.
We present a remarkable improvement in the efficiency of AlGaN deepultraviolet light-emitting diodes (LEDs) enabled by the coupling of localized surface plasmon resonance (LSPR) mediated by a high-density array of Al nanoparticles (NPs). The Al NPs with an average diameter of ∼40 nm were uniformly distributed near the Al 0.43 Ga 0.57 N/Al 0.50 Ga 0.50 N multiple quantum well active region for coupling 285 nm emission by block copolymer lithography. The internal quantum efficiency is enhanced by 57.7% because of the decreased radiative recombination lifetime by the LSPR. As a consequence, the AlGaN LEDs with an array of Al NPs show 33.3% enhanced electroluminescence with comparable electrical properties to those of reference LEDs without Al NPs.
Semiconductor nanowires are attractive
building blocks of optoelectronics
due to high efficiency and optical controllability. In particular,
the mutual controllability of wavelength and polarization of light
is essential for versatile applications such as displays, precise
metrology, and bioimaging. We present quantum wire network emitters
embedded in a single microrod capable of exhibiting orthogonally polarized
dual-wavelength visible light at room temperature. The InGaN/GaN shell
layers were grown on a single hexagonal GaN core microrod, spontaneously
forming site-selective In-rich InGaN quantum wires on each edge between
the nonpolar facets as well as each boundary between the nonpolar
and semipolar facets. The orthogonally self-arranged, two sets of
six quantum wires formed on the edges and the boundaries showed efficient
violet and blue-green color emissions with strong linear polarization
parallel and perpendicular to the c-axis at room
temperature, respectively. This intriguing emission from a single
microrod allows us to mutually manipulate the color and the polarization
of light, which would be beneficial for photonic applications with
unprecedented controllability and functionality.
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