Enhancement of external quantum efficiency of LEDs by fabricating photonic crystal in ITO p-contact layer

Abstract

Light-emitting diodes (LEDs) have the potential to become the main light source for the advantages of low energy consumption, being environmental friendly and long lifetime. However so far the brightness of LEDs is not sufficient for many applications due to low light extraction efficiency resulted from total internal reflection of the emitted light at semiconductor/air interface. To overcome this problem, fabricating 2-dimensional photonic crystals (PhCs) on the surfaces of LEDs is considered as one of the most effective ways. At present, the method of fabricating PhCs is primarily through e-beam lithography and ion-beam etching. Such processes are complicated and unsuitable for low cost mass production. In this paper we propose a novel method of using holographic and wet etching processes to fabricate PhCs in p-contact ITO layers of LEDs. The PhC patterns are firstly fabricated in photoresist layers coated on LEDs, using holographic approach, then acid solution are used to transfer the patterns into ITO layers. The experiments of adopting different etching solutions and etching rates were carried out and the results were compared, in order to find out the best etching condition. Experimental results demonstrate that solution HCl : HNO3 : H2O made less damage to photoresist mask and can better control the etching depth in ITO. PhCs with different lattice constant and depth were fabricated to obtain the best PhC parameters for higher light extraction. 30% increase of external quantum efficiency has been achieved in the experiment.