Light intensity and efficiency enhancement of n-ZnO/NiO/p-GaN heterojunction-based white light-emitting diodes using micro-pillar array

Abstract

This study presents a unique method of enhancing light intensity and efficiency of light-emitting diodes (LEDs) by incorporating micro-pillars' array on top of the substrate layer. The micro-pillars' array on the substrate layer increases the light extraction efficiency, which in turn increases the external quantum efficiency (EQE) and output light intensity of the LEDs. The simulation works have been conducted using finite difference time domain method. To achieve white LED, we inserted a thin NiO layer inside the n-type ZnO and p-type GaN layers. The basic n-ZnO/NiO/p-GaN heterojunction-based LED showed an EQE of 10.99% as the effective refractive index of the LED structure was 1.48. The EQE of the basic LED was further increased by engraving micro-pillars' array on the top of the substrate layer. A maximum EQE of 12.8% was achieved for Pillar-2 type micro-pillars array having pillars' width and height of 2 mu m and 0.2 mu m where effective refractive index of the LED structure was 1.38. On the contrary, the peak electroluminescence light intensity was 2.22 times higher in Pillar-2 type micro-pillars' array-based LED than the basic LED. Due to the excellent electroluminescence spectrum and intensity profile, the proposed Pillar-2 type micro-pillars' array engraved LED can be considered as a potential candidate for white LED.