Light Guide Layer Thickness Optimization for Enhancement of the Light Extraction Efficiency of Ultraviolet Light–Emitting Diodes

Abstract

Challenges related to deep-ultraviolet light-emitting diode substrates include material costs and lattice mismatch. Sapphire substrates are commonly used, although their high refractive index can result in the total internal reflection of light whereby some light is absorbed, reducing light extraction efficiency (LEE). In this study, we proposed an optimal thickness value of a sapphire substrate light guide layer through first-order optical design and used the optical simulation software Ansys SPEOS to assess and refine its effect on LEE. AlGaN ultraviolet-C light-emitting diode (UV-C LED) wafers with a substrate thickness of 150–700 μm were used. The simulation proceeded under a UV-C LED center wavelength of 275 nm to determine the optimal thickness of the light guide layer. Finally, the experimental results demonstrated that a light guide layer thickness of 150 μm resulted in a reference output power of 13.53 mW, and an increased thickness of 600 um resulted in output power of 20.58 mW. The LEE can therefore be increased by 1.52 times through light guide layer thickness optimization.