Improvement of Light Extraction in Deep Ultraviolet GaN Light Emitting Diodes with Mesh P-Contacts

Shiou-Yi Kuo,Tien-Chang Lu,Zhen-Ting Huang,Chia-Jui Chang

doi:10.3390/app10175783

Abstract

One of the main reasons that the emission efficiency of GaN-based light-emitting diodes (LEDs) decreases significantly as the emission wavelength shorter than 300 nm is the low light extraction efficiency (LEE). Especially in deep ultra-violet (DUV) LEDs, light propagating outside the escape cone and being reflected back to the semiconductor or substrate layer is absorbed not only by active layers but also by p-type layers with narrower bandgaps and electrodes that are neither transparent nor reflective of the DUV wavelength. In this report, we propose a DUV LED structure with mesh p-GaN/indium-tin-oxide (ITO) contacts and a Ti/Al/Ni/Au layer as a reflective layer to improve LEE. The mesh p-GaN/ITO DUV LED showed an output power of 12% higher than that from the conventional DUV LED due to the lower light absorption at 280 nm.

Highlights

Light-emitting diodes (LEDs) have rapidly developed into the main light source in the world because of the high emission efficiency of the blue band from InGaN/GaN multiple quantum wells (MQWs) grown on sapphire substrates [1,2,3,4,5,6]
By carefully arranging the mesh configuration, we can significantly improve the emission efficiency and increase the output power of the deep ultra-violet (DUV) light-emitting diodes (LEDs) with an emission wavelength at 280 nm
Trimethylgallium (TMGa), trimethylaluminum (TMAl) for the group-III element, and ammonia (NH3 ) for the group-V element were used in the low-pressure metal-organic chemical vapor deposition (MOCVD) to grow the DUV LED structure on an AlN template grown (0001)-oriented c-plane sapphire substrate

Summary

Introduction

Light-emitting diodes (LEDs) have rapidly developed into the main light source in the world because of the high emission efficiency of the blue band from InGaN/GaN multiple quantum wells (MQWs) grown on sapphire substrates [1,2,3,4,5,6]. There is some controversy about the decline in the efficiency of blue GaN LEDs, under certain controlled operating conditions, the state-of-the-art external quantum efficiency (EQE) has reached approximately 75% [7]. The AlInGaN alloy composition can be adjusted to control its emission wavelength. The emission wavelength corresponding to the bandgap of the alloy can be tuned from the infrared (IR), visible to ultraviolet (UV) bands [8,9]. When the emission wavelength is adjusted to the green and ultraviolet bands, the emission efficiency of GaN-based

Methods

Discussion

Conclusion