Using a Multi-Layer Stacked AlGaN/GaN Structure to Improve the Current Spreading Performance of Ultraviolet Light-Emitting Diodes.

Yanli Wang,Wenkai Yue,Xiaowei Zhou,Yue Hao,Peixian Li,Xinyu Zhang,Shengrui Xu,Jinxing Wu

doi:10.3390/ma13020454

Abstract

To obtain excellent current spreading performance of ultraviolet light-emitting diodes (UVLEDs), a 60-period stacked Si modulation-doped n-AlGaN/u-GaN structure is proposed to replace the traditional n-AlGaN structure. The high-resolution X-ray diffraction ω-scan rocking curves show that the periodic growth of AlGaN and GaN layers plays a positive role in reducing dislocation density. Compared with the conventional UV light-emitting diodes (LEDs), light emission micrographs of devices with a multi-layer stacked n-AlGaN/u-GaN structure reveal higher brightness and a more uniform distribution. In addition, the output power and external quantum efficiency under a 20-mA injection current are increased by 22% and 26.5%, respectively. Experimental and simulation results indicate that a multi-layer stacking structure can alleviate the current crowding effect in four ways: (1) a reduction in dislocation density; (2) replacement of quasi-two-dimensional electron transport with electronic bulk transport to enhance electron mobility; (3) an increase in electron concentration without improving the impurity concentration; and (4) a weakening of the electron scattering effect by reducing the impurity concentration.

Highlights

Ultraviolet light-emitting diodes (UV-LEDs) have received positive attention from scholars and companies around the world to due to their properties, such as: high switching speeds; lack of heat radiation; their non-toxic, uniform illumination; high energy; and long service life [1,2,3,4]
A 22% increase in the output power of Sample B suggests that the well-distributed current and low dislocation density are beneficial to improving the luminous efficiency
Two different devices were grown by Metal Organic Chemical Vapor Deposition

Summary

Introduction

Ultraviolet light-emitting diodes (UV-LEDs) have received positive attention from scholars and companies around the world to due to their properties, such as: high switching speeds; lack of heat radiation; their non-toxic, uniform illumination; high energy; and long service life [1,2,3,4]. Since the positive and negative electrodes in the lateral UV-LEDs are located on the same side, the current distribution of the whole device is severely uneven [6]. The in-plane non-uniformity of luminous intensity and local overheating may appear in the quantum well regions [7,8], reducing the internal quantum efficiency and reliability of devices [6]. Because the current crowding effect occurs near the electrodes, the optical loss caused by metal electrodes’ absorption will cut down the optical extraction efficiency [9]. The current crowding effect causes the forward voltage to rise, lowering the electro-optical conversion

Methods

Results

Conclusion