Improvement in Light Output of Ultraviolet Light-Emitting Diodes with Patterned Double-Layer ITO by Laser Direct Writing.

Jie Zhao,Shengjun Zhou,Jinfeng Hu,Hui Wan,Jiahao Miao,Xinghuo Ding

doi:10.3390/nano9020203

Abstract

A patterned double-layer indium-tin oxide (ITO), including the first unpatterned ITO layer serving as current spreading and the second patterned ITO layer serving as light extracting, was applied to obtain uniform current spreading and high light extraction efficiency (LEE) of GaN-based ultraviolet (UV) light-emitting diodes (LEDs). Periodic pinhole patterns were formed on the second ITO layer by laser direct writing to increase the LEE of UV LED. Effects of interval of pinhole patterns on optical and electrical properties of UV LED with patterned double-layer ITO were studied by numerical simulations and experimental investigations. Due to scattering out of waveguided light trapped inside the GaN film, LEE of UV LED with patterned double-layer ITO was improved as compared to UV LED with planar double-layer ITO. As interval of pinhole patterns decreased, the light output power (LOP) of UV LED with patterned double-layer ITO increased. In addition, UV LED with patterned double-layer ITO exhibited a slight degradation of current spreading as compared to the UV LED with a planar double-layer ITO. The forward voltage of UV LED with patterned double-layer ITO increased as the interval of pinhole patterns decreased.

Highlights

Ultraviolet (UV) light-emitting diodes (LEDs) have attracted considerable attention due to their potential applications in sterilization, water purification, photocatalyst, and solid-state lighting [1,2,3,4,5,6,7,8]
We investigated the effect of interval of pinhole patterns on current spreading of UV LED with double-layer ITO using SimuLED commercial software package
The first unpatterned current spreading layer and the second patterned light extracting layer were combined into a patterned double-layer ITO to improve current spreading and light extraction efficiency (LEE) of UV LEDs

Summary

Introduction

Ultraviolet (UV) light-emitting diodes (LEDs) have attracted considerable attention due to their potential applications in sterilization, water purification, photocatalyst, and solid-state lighting [1,2,3,4,5,6,7,8]. Several kinds of transparent conductive layer such as metal nanowires [13,14,15,16], graphene [17,18,19], carbon nanotubes [20,21], and conductive polymers [22,23,24] have been reported to improve the current spreading of LEDs. For top-emitting LEDs, indium-tin-oxide (ITO) has been widely used to increase current spreading uniformity over the entire active region due to its high optical transmittance and excellent electrical conductivity [25,26,27]. Patterned ITO has been shown to degrade the current spreading performance of UV LED due to an increase in sheet resistance [39,40,41]. Effects of interval of pinhole patterns on the optical and electrical characteristics of UV LED with patterned double-layer ITO were studied in detail using numerical simulations and experimental investigations

Materials and Methods

Results and Discussion

Findings

Conclusions