Flower-Like Internal Emission Distribution of LEDs with Monolithic Integration of InGaN-based Quantum Wells Emitting Narrow Blue, Green, and Red Spectra

Kwanjae Lee,Ilgyu Choi,Cheul-Ro Lee,Tae-Hoon Chung,Kwang-Un Jeong,Yoon Seok Kim,Dong Chul Chung,Jin Soo Kim

doi:10.1038/s41598-017-07808-2

Abstract

We report a phosphor-free white light-emitting diodes (LED) realized by the monolithic integration of In0.18Ga0.82N/GaN (438 nm, blue), In0.26Ga0.74N/GaN (513 nm, green), and In0.45Ga0.55N/In0.13Ga0.87N (602 nm, red) quantum wells (QWs) as an active medium. The QWs corresponding to blue and green light were grown using a conventional growth mode. For the red spectral emission, five-stacked In0.45Ga0.55N/In0.13Ga0.87N QWs were realized by the so-called Ga-flow-interruption (Ga-FI) technique, wherein the Ga supply was periodically interrupted during the deposition of In0.3Ga0.7N to form an In0.45Ga0.55N well. The vertical and lateral distributions of the three different light emissions were investigated by fluorescence microscope (FM) images. The FM image measured at a focal point in the middle of the n-GaN cladding layer for the red-emitting LED shows that light emissions with flower-like patterns with six petals are periodically observed. The chromaticity coordinates of the electroluminescence spectrum for the white LEDs at an injection current of 80 mA are measured to be (0.316, 0.312), which is close to ideal white light. In contrast with phosphor-free white-light-emitting devices based on nanostructures, our white light device exhibits a mixture of three independent wavelengths by monolithically grown InGaN-based QWs, thus demonstrating a more facile technique to obtain white LEDs.

Highlights

Have been investigated to extend emission wavelengths to long-visible wavelengths, including orange and red spectral ranges, especially for the fabrication of white light sources
In the color-coded mode (CCM)-transmission electron microscope (TEM) image of the red quantum wells (QWs) shown in Fig. 2(d), the green region is more indistinct over a large area than in those of the blue and green QWs
In the fluorescence microscope (FM) image obtained from the middle of the n-GaN cladding layer in the RLED, the shape of the light emission observed mostly around the lens-shaped patterns (LSPs) exhibited a flower shape with six petals

Summary

Introduction

Have been investigated to extend emission wavelengths to long-visible wavelengths, including orange and red spectral ranges, especially for the fabrication of white light sources. Commercial blue or green LEDs are based on InGaN/GaN QW structures, and obtaining long-visible wavelengths over ~550 nm using QWs is a significant achievement. Phosphor-free WLEDs with two or three emission wavelengths have been realized using InGaN/GaN multiple QWs (MQWs) with different In contents[17, 18], the blue, green, and red emissions were not clearly distinguished in their electroluminescence (EL) spectra. We successfully realized phosphor-free WLEDs with monolithically grown InGaN-based MQWs with clearly distinguished blue, green, and red spectra. InGaN/GaN MQWs with blue and green emissions were grown using a conventional growth method, wherein the In, Ga, and N sources were simultaneously supplied to grow the InGaN wells. The vertical and lateral distributions of the samples’ luminescence were investigated using fluorescence microscope (FM) images measured by changing the focal point (FP)

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Results

Conclusion