Abstract
We report a hexagonal GaN nanorod-based two-dimensional photonic crystal (PhC) slab for phosphor-conversion white light emitting devices analyzed by three-dimensional finite-difference time-domain simulation; this slab has a broad reflection band at yellow wavelength with low Fabry-Pérot background at normal incidence. For practical use as a wavelength-selective reflector, a buffer layer under the PhC slab is employed to sustain the nanorods in the PhC slab. However, we observed that the buffer layer placed below the slab destroys the broad reflection band due to evanescent coupling of electromagnetic field in the slab and the buffer layer. By introducing small-sized base pillars between the slab and the buffer layer, we could decouple the interaction between the slab and the buffer layer and maintain the broad reflection band without any unexpected dips. Since this GaN nanorod-based PhC slab is designed for practical light emitting devices by considering dielectric and transparent conducting layers, this structure is directly applicable for developing hybrid white light emitting devices having both an (active) blue-color-emitting nanorod emitters and a (passive) normal reflector of phosphor emission.
Highlights
We report a hexagonal GaN nanorod-based two-dimensional photonic crystal (PhC) slab for phosphorconversion white light emitting devices analyzed by three-dimensional finite-difference time-domain simulation; this slab has a broad reflection band at yellow wavelength with low Fabry-Pérot background at normal incidence
We investigated the 2D PhC slab composed of GaN nanorod array to establish a broadband reflector which provides high and broad reflection at yellow wavelength region and high transmission at blue wavelength region
The computational domain is enclosed by Bloch boundary conditions on the four sidewalls and by perfectly matched layers on the top and bottom displaced from top and bottom of PhC slab by 2100 nm and 1400 nm, respectively
Summary
We report a hexagonal GaN nanorod-based two-dimensional photonic crystal (PhC) slab for phosphorconversion white light emitting devices analyzed by three-dimensional finite-difference time-domain simulation; this slab has a broad reflection band at yellow wavelength with low Fabry-Pérot background at normal incidence. By introducing small-sized base pillars between the slab and the buffer layer, we could decouple the interaction between the slab and the buffer layer and maintain the broad reflection band without any unexpected dips Since this GaN nanorod-based PhC slab is designed for practical light emitting devices by considering dielectric and transparent conducting layers, this structure is directly applicable for developing hybrid white light emitting devices having both an (active) blue-color-emitting nanorod emitters and a (passive) normal reflector of phosphor emission. The rod-based structure was chosen because it is preferable to make low Fabry-Pérot background as it generally has much lower filling fraction than conventional hole array in dielectric layer This wavelength-selective reflection property and the textured structure of our GaN nanorod-based PhC slab can simultaneously improve the color rendering and extraction efficiency of the phosphor-conversion white LEDs by enhancing the reflection of phosphor emission, in contrast to the previously proposed hole array on GaN-based LEDs which were used to enhance only the extraction efficiency of the LEDs10,11. We confirmed that the introduction of a sapphire substrate, a mask material, and ITO do not significantly affect to the broad reflection band
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