Simulations of light extraction and light propagation properties of light emitting diodes featuring silicon carbide substrates
Journal
Optical Materials
Journal Volume
35
Journal Issue
6
Pages
1236-1242
Date Issued
2013
Author(s)
Abstract
Although silicon carbide (SiC) possesses excellent material properties and is a good candidate to replace sapphire as the substrate material for high-power light emitting diodes (HP-LEDs), the light extraction behavior of SiC substrate-based gallium nitride (GaN) LEDs had not been reported in detail previously. In this study, we measured the optical properties of SiC substrates and determined their effects on SiC substrate-based LEDs. Because the optical constants of SiC are very different from those of sapphire substrates, the light propagating and light extracting behavior of SiC substrate-based LEDs differs dramatically from that of traditional sapphire substrate-based LEDs. Herein, we used rigorous coupled-wave analysis and finite-difference time domain methods to systematically analyze the light propagating behavior of flip-chip and conventional-type SiC substrate-based LEDs. Our measured and simulated data revealed that the absorption of the SiC substrate would seriously affect the light extraction efficiency of flip-chip SiC LEDs. For the conventional-type LEDs, on the other hand, because the refractive index of SiC is greater than that of GaN, light readily propagates through the GaN-SiC interface into the SiC substrate to form the SiC substrate guided mode, which cannot be extracted. Therefore, maximizing the first direct extraction light from conventional-type SiC LEDs would be the most effective approach toward increasing the light extraction efficiency. Accordingly, we analyzed some periodic structures that enhanced the light extraction efficiency of SiC substrate-based LEDs. © 2013 Elsevier B.V. All rights reserved.
Type
journal article