Large enhancement of light extraction efficiency in AlGaN-based nanorod ultraviolet light-emitting diode structures

Han-Youl Ryu

doi:10.1186/1556-276x-9-58

Abstract

Light extraction efficiency (LEE) of AlGaN-based nanorod deep ultraviolet (UV) light-emitting diodes (LEDs) is numerically investigated using three-dimensional finite-difference time-domain simulations. LEE of deep UV LEDs is limited by strong light absorption in the p-GaN contact layer and total internal reflection. The nanorod structure is found to be quite effective in increasing LEE of deep UV LEDs especially for the transverse magnetic (TM) mode. In the nanorod LED, strong dependence of LEE on structural parameters such as the diameter of a nanorod and the p-GaN thickness is observed, which can be attributed to the formation of resonant modes inside the nanorod structure. Simulation results show that, when the structural parameters of the nanorod LED are optimized, LEE can be higher than 50% and 60% for the transverse electric (TE) and TM modes, respectively. The nanorod structure is expected to be a good candidate for the application to future high-efficiency deep UV LEDs.PACS41.20.Jb; 42.72.Bj; 85.60.Jb

Highlights

Ultraviolet (UV) light-emitting diodes (LEDs) based on AlGaN materials have attracted great attention for various applications in daily lives and industry [1,2,3,4]
In this work, we investigated Light extraction efficiency (LEE) of AlGaN-based nanorod deep UV LEDs emitting at 280 nm using 3-D finite-difference timedomain (FDTD) simulations
When the LED structure is replaced from planar to nanorod structures, LEE for the transverse magnetic (TM) mode was found to increase from 0.1% to approximately 60%

Summary

Introduction

Ultraviolet (UV) light-emitting diodes (LEDs) based on AlGaN materials have attracted great attention for various applications in daily lives and industry [1,2,3,4]. Efficiency of current AlGaN-based deep UV LEDs is too low to replace UV lamps. Light extraction efficiency (LEE) of AlGaN-based deep UV LEDs has been thought to be quite low owing to the strong UV light absorption in the p-GaN contact layer and the unique anisotropic optical polarization property in AlGaN quantum wells (QWs) with high Al composition [5]. In AlGaN QWs, light is emitted as either TE or TM mode, and the portion of the TM mode increases as the Al composition increases or emission wavelength decreases [6,7,8].

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