Suppressing spontaneous polarization of p-GaN by graphene oxide passivation: augmented light output of GaN UV-LED.

Hyun Jeong,Hee Jin Jeong,Eun-Kyung Suh,Sunhye Yang,Yeong Hwan Ahn,Ho Young Kim,Young Hee Lee,Doo Jae Park,Mun Seok Jeong,Kang-Jun Baeg,Sae June Park,Seung Yol Jeong,Joong Tark Han,Geon-Woong Lee,Sooyeon Jeong,Hyeon Jun Jeong

doi:10.1038/srep07778

Abstract

GaN-based ultraviolet (UV) LEDs are widely used in numerous applications, including white light pump sources and high-density optical data storage. However, one notorious issue is low hole injection rate in p-type transport layer due to poorly activated holes and spontaneous polarization, giving rise to insufficient light emission efficiency. Therefore, improving hole injection rate is a key step towards high performance UV-LEDs. Here, we report a new method of suppressing spontaneous polarization in p-type region to augment light output of UV-LEDs. This was achieved by simply passivating graphene oxide (GO) on top of the fully fabricated LED. The dipole layer formed by the passivated GO enhanced hole injection rate by suppressing spontaneous polarization in p-type region. The homogeneity of electroluminescence intensity in active layers was improved due to band filling effect. As a consequence, the light output was enhanced by 60% in linear current region. Our simple approach of suppressing spontaneous polarization of p-GaN using GO passivation disrupts the current state of the art technology and will be useful for high-efficiency UV-LED technology.

Highlights

GaN-based ultraviolet (UV) LEDs are widely used in numerous applications, including white light pump sources and high-density optical data storage
One technological bottleneck in GaN LED is strong spontaneous electric polarization formed in p-GaN, leading to poor hole injection rate, heavily p-doped GaN has been successfully grown on c-plane sapphire substrates[3,4]
The prepared graphene oxide (GO) nanosheet solution was spincasted onto the UV-LED12

Summary

Introduction

GaN-based ultraviolet (UV) LEDs are widely used in numerous applications, including white light pump sources and high-density optical data storage. One technological bottleneck in GaN LED is strong spontaneous electric polarization formed in p-GaN (hole transport layer), leading to poor hole injection rate, heavily p-doped GaN has been successfully grown on c-plane sapphire substrates[3,4]. Owing to this polarization, hole carriers in p-GaN are locally bound by potential gradient, preventing them from contributing to the radiative recombination in multiple quantum wells (MQWs)[5]. We propose a simple and effective method to suppress spontaneous polarization of p-GaN transport layer by spin-casting GO layers on the conventionally fabricated UV-LED to eventually enhance the light output power

Methods

Results

Conclusion