Optimization on the design of nano-patterned ZnS:Cu LED surface using FDTD simulation

Abstract

Communication technology is one of the most important parts of human history and is fast developing. Visible Light Communication (VLC) can be categorized as a Light Fidelity (Li-Fi) communication that uses visible light through a Light Emitting Diode (LED) to transfer data and information. Even though LEDs are considered as very good light sources, they also have problems with effectiveness, which is influenced by their surface structures. The LEDs must also be able to focus the transmitted data and greatly reduce the signal-to-noise ratio. One of the problems encountered with LEDs is the presence of Total Internal Reflection (TIR) due to the large difference in refractive index between the LED and air, which causes photons to be trapped in the LED. Some trapped photons' energy may change into heat, thus reducing the LED's Light Extraction Efficiency (LEE). Using nanopatterns on the surface of LEDs is one way to reduce TIR on LEDs and enhance photon extraction from LEDs. Many parameters can influence the performance of nanopatterns on LEDs, so modelling efforts are needed before fabrication to save time and cost. Ansys Lumerical FDTD can be used to simulate and model the effects of nanopatterns on LED surfaces on LEE and beam focusing effect. In this study, simulations were carried out using Ansys Lumerical FDTD with variations in nanopattern shape parameters in the form of grating, blaze grating, triangular grating, and hemisphere. Apart from that, variations were also made to the height and width parameters of the grating to see the effect of these parameters on the efficiency of the LED. The FDTD simulation codes were validated using the Ansys database. The optimization results show that the most optimum shape is the grating nanopattern with a width of 216 nm and a height of 300 nm, which produces a peak wavelength of 480 nm in the far field pattern and has the highest increase in the LEE of 300 times in ±15° and 5500 times in ±5°. The huge spike in LEE enhancement at ±5° indicates that the nanopattern caused a focusing effect. The simulation results were compared using previous experimental data of Fabricated ZnS:Cu LED. It is shown that the simulation results are in line with the experimental data. The result shows that the simulation is very useful in designing the nano-patterned ZnS:Cu LED surface to achieve the best performance in the LEE and LED focusing effect for a specific application such as the VLC.