Reflectance of a reflective photonic crystal p-contact layer for improving the light-extraction efficiency of AlGaN-based deep-ultraviolet light-emitting diodes

Abstract

We utilized the finite-difference time-domain method (FDTD) to investigate the reflectance of an air void photonic crystal (PhC) on the p-electrode of an AlGaN-based deep ultraviolet (DUV) light-emitting diode (LED). Firstly, a transparent p-AlGaN layer with cylindrical air voids on a Ni(1nm)/Al(140nm) metal electrode was optimized to maximize the reflectance at normal incidence. It was shown that by having the optimum AlGaN PhC on the metal electrode, the reflectance as a function of the angle of incidence was advantageously redistributed to increase LEE. The calculated angle-dependent reflectances were converted to average reflectance considering the power distribution of dipole sources in the TE and TM modes. The average reflectances of a reference structure and the PhC structure for the TM mode at wavelengths around 283 nm were 77.1 and 85.2%, respectively. Thus, an incremental increase of 8% in average reflectance for the TM mode was obtained by adopting the optimized PhC. Secondly, we investigated a PhC with air voids in two different layers, a p-GaN layer and a p-AlGaN layer on the Ni/Al. The calculated average reflectances at 283 nm were 38% and 42% for the TE and TM modes, respectively, when the thickness of the p-GaN layer was 70 nm. The average reflectances for the TE and TM modes with a uniform 70nm thick p-GaN layer without a PhC were 4.2 and 3.6%, respectively. This clearly shows that the optimized PhC can reduce light absorption in both the p-GaN layer and the metal electrode.

Design of photonic crystals for light‐emitting diodes

“…Yun et al. investigated the relationship between the reflectance of gap PC on AlGaN‐based DUV LEDs p‐electrodes and PC structural parameters to improve LEE 103 . The structure is shown schematically in Figure 29A,B, with a hexagonal lattice arrangement.…”

“…Embedded PC LEDs p-electrodes and PC structural parameters to improve LEE. 103 The structure is shown schematically in Figure 29A,B, with a hexagonal lattice arrangement. The optimal parameters of the PC were calculated by simulation, and then the improvement of the PC structure on the LED performance was observed.…”

Surface-emitting photonic crystal terahertz quantum cascade laser adopting uniform triangular prism photonic crystal with a double-metal waveguide

“…We utilize FDTD to analyze unit cells consisting of the multilayer PhC slabs. [21][22][23] Boundaries of  z-axes of the unit cell are set up with the convolutional perfectly matched layer (CPML). Other boundaries are all set up by the PBCs.…”

Investigation of Light-Extraction Efficiency of Flip-Chip AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes Adopting AlGaN Metasurface

“…Figure 1(b) and (c) show cross-sectional views of a YZ-plane cutting the middle of the x-axis and an XYplane cutting the middle of the cylinder's height, respectively. The constant horizontal wavenumber approach is utilized to efficiently analyze the constructed unit cell [17]- [19]. The unit cell's each plane at the end of +x, -x, +y, and -y directions adopt periodic boundaries.…”