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

Abstract

Our study proposes a technique to enhance light extraction efficiency of light emitting diodes (LEDs) by incorporating various micro-/nanolens arrays (MNLAs) on the substrate layer, which in turn increases the external quantum efficiency (EQE) of the LEDs. To simulate the LEDs, we utilized the finite difference time domain method. To achieve a white LED, we inserted a thin layer of NiO at the interface between the n-type ZnO and the p-type GaN. The basic n-ZnO/NiO/p-GaN heterojunction-based LED exhibited an EQE of 10.99% where the effective refractive index of the LED structure was 1.48. The EQE was further increased by engraving various planoconvex or planoconcave MNLA on the top surface of the substrate layer. A maximum EQE of 12.4% was achieved for convex-1 type (lens height of 0.5 μm and radius of 0.4 μm) elliptical lens engraved LED where the effective refractive index was 1.4. In addition, the peak electroluminescence (EL) light intensity of convex-1 lens-based LED was twice than the light intensity observed in basic LED. Because of excellent EL spectrum and significant amount of light throughout the visible spectrum, the proposed convex-1 structure-based LED can be considered as a prospective candidate for white LED.