Highly efficient InGaN/GaN LEDs with double-sided textured surfaces and omni-directional mirror structure

Abstract

The p-side-up GaN light-emitting diode (LED) were fabricated using a combination of omni-directional reflector (ODR) and double-sided textured surface (both p-GaN and undoped-GaN) techniques. An Essential Macleod program was used to simulate the optimum thickness of the ODR structure. The reflectivity value of ODR structure used in work can reach 99%. On the top-side textured surface, the p-type GaN with hexagonal cavities was grown under low temperature conditions using metalorganic chemical vapor deposition. The GaN LED with a suitable low-temperature p-GaN cap layer thickness was also studied. Experimental results indicate that the LED sample with a 200-nm hexagonal cavity GaN layer on the surface exhibits a 50% enhancement in luminance intensity. For a small chip size of 250 µm×500 µm, the luminance efficiency can be improved from 23.2 to 28.2% at 20 mA. However, the luminance efficiency with a larger chip size of 1mm×1mm can be improved from 19.8 to 28.9%. This indicates that the thin-film structure can enhance the light extraction efficiency of GaN-based LEDs, especially for the large chip sizes.