Enhancement of light extraction of GaN light-emitting diode using opals layer

Abstract

Light emitting diodes (LEDs) based on indium gallium nitride (InGaN) have been used widely in lighting applications and have shown great potential with high wall-plug efficiency and low manufacturing cost. However, one of the roadblocks in achieving higher light-extraction efficiency is total internal reflection, which prevents a majority of the photons from being extracted from the LEDs. The objective of this paper is to investigate measures for improving LED chip efficiency. Here, a high efficiency LED structure has been theoretically demonstrated using an infiltrated opal layer. A layer of indium-tin oxide (ITO) infiltrated opals was deposited on the surface of the LED chips as the light extraction layer in order to enhance the light extraction efficiency. Opals of similar radius periodically arranged on the structure will work as a rough surface. By enhancing the light extraction angle, the spontaneous emission from the active region can be emitted vertically. At the same time, opals with different radius and different refractive indexes are also studied. ITO, as the infiltration, is used to provide good lateral current spreading. The plane wave expansion (PWE), finite difference time domain (FDTD), and rigorous coupled wave analysis (RCWA) methods are used to calculate the energy band structures and the extraction efficiency of the infiltrated opals layer. The scanning method and the Monte Carlo method are employed to optimize the structural parameters of the infiltrated opal layer. The infiltrated opals layer on the LED shows a high light extraction efficiency of over 60%.