Top Transmission Grating GaN LED Simulations for Light Extraction Improvement
Copyright © 2011 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. This paper is also available at http://dx.doi.org/10.1117/12.871595.
We study the top transmission grating’s improvement on GaN LED light extraction efficiency. We use the finite difference time domain (FDTD) method, a computational electromagnetic solution to Maxwell’s equations, to measure light extraction efficiency improvements of the various grating structures. Also, since FDTD can freely define materials for any layer or shape, we choose three particular materials to represent our transmission grating: 1) nonlossy p-GaN, 2) lossy indium tin oxide (ITO), and 3) non-lossy ITO (α=0). We define a regular spacing between unit cells in a crystal lattice arrangement by employing the following three parameters: grating cell period (Α), grating cell height (d), and grating cell width (w). The conical grating model and the cylindrical grating model are studied. We also presented in the paper directly comparison with reflection grating results. Both studies show that the top grating has better performance, improving light extraction efficiency by 165%, compared to that of the bottom reflection grating (112%), and top-bottom grating (42%). We also find that when grating cells closely pack together, a transmission grating maximizes light extraction efficiency. This points our research towards a more closely packed structure, such as a 3-fold symmetric photonic crystal structure with triangular symmetry and also smaller feature sizes in the nano-scale, such as the wavelength of light at 460 nm, half-wavelengths, quarter wavelengths, etc.
Simeon Trieu, Xiaomin Jin, Ashton Ellaboudy, Bei Zhang, Xiang-Ning Kang, Guo-Yi Zhang, Xiong Chang, Wei Wei, Sun Yong Jian, and Fu Xing Xing. "Top Transmission Grating GaN LED Simulations for Light Extraction Improvement" Proceedings of SPIE 2011, San Francisco, CA.. Jan. 2011.
Available at: http://works.bepress.com/xjin/32