Structural Parameter Optimization and Far-Field Characteristics of GaN-Based Micro-LEDs for RGB Emission Using FDTD Simulation

Abstract

As the core light source for next-generation display technology, Micro-LEDs’ light extraction efficiency (LEE) and far-field distribution characteristics directly determine display performance. However, existing research has primarily focused on parameter optimization for a single wavelength (blue light), lacking a systematic analysis of wavelength dependence across the RGB color system. In this paper, based on Ansys Lumerical FDTD Solutions and employing a multipole averaging method, we systematically investigated the structural optimization and far-field characteristics of GaN-based Micro-LEDs with a pixel diameter of 3 μm at three wavelengths: 460 nm (blue light), 530 nm (green light), and 620 nm (red light). The main work and conclusions include: (1) By comparing the LEE under conditions with 1–20 dipoles, it was determined that 12 dipoles can achieve stable convergence for all three wavelengths, and it was found that the LEE for red light is generally about 15–20% higher than that for blue light. (2) Based on cavity interference theory, the p-GaN thickness (50–500 nm) was scanned for each of the three colors, yielding optimal thicknesses of 190 nm (blue), 200 nm (green), and 260 nm (red), respectively, and revealing the wavelength-dependent pattern of interference peak position shifts. (3) By scanning sidewall angles from 0° to 60°, the optimal angles for the three colors were determined to be 32° (blue light), 36° (green light), and 30° (red light), with peak LEE_top values reaching 0.60, 0.66, and 0.69, respectively, which are highly consistent with existing research. (4) By comparing the far-field distributions with and without five pairs of TiO₂/SiO₂ DBR sidewall reflectors, we found that the DBRs increased the peak intensity by 72% for blue light and 31% for red light, but provided almost no gain for green light, revealing the differing effects of DBR angle dependence on different wavelengths. This study provides wavelength-dependent optimization guidelines for the pixel structure design of full-color Micro-LED displays.