Enhanced light extraction efficiency of Eu-related emission from a nano-patterned GaN layer grown by MOCVD

A Lesage,D Timmerman,Y Fujiwara,T Gregorkiewicz,T Inaba

doi:10.1038/s41598-019-40971-2

A Lesage, D Timmerman + Show 3 more

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https://doi.org/10.1038/s41598-019-40971-2

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Journal: Scientific Reports	Publication Date: Mar 12, 2019
Citations: 3	License type: open-access

Affiliation: University of Amsterdam, Osaka University

Abstract

Eu-doped GaN is a promising material for the active layer in red light emitting diodes. Although the output power of LEDs based on GaN:Eu has been increasing by a combination of structural and growth optimizations, there is still a significant limitation resulting from a poor light extraction efficiency, typical for high refractive index materials. Here we studied nanostructuring of the top of the optical active layer by nano-cubes for enhancement of the light extraction efficiency, and its effect on the optical emission characteristics. By etching nano-cubes into the active layer, we observed an increase in directional light output power of Eu3+ ions of up to 60%, as well as a grating effect. Simultaneously, the absorption of excitation light into the optical active layer was improved, leading to a 12.8 times increase of output power per available Eu3+ ion.

Highlights

GaN-based efficient red light emitters are a key development to complement the already available blue and green colors, and realize monolithically produced full-color displays
We have studied the directional emission of these structures and observed an increase of the light output of 60% for the structured samples as compared to the reference
We have fabricated GaN:Eu layers, which were nano-patterned with a square lattice array of cubes, and studied effect of this on emission characteristics by PL spectroscopy

Summary

Introduction

GaN-based efficient red light emitters are a key development to complement the already available blue and green colors, and realize monolithically produced full-color displays. The pattern consists of cubes organized in a square lattice and was formed by a nano-imprint lithography process This particular choice of nano-patterning has been used, as dielectric structures of these dimensions are well-known to show nano-resonator behavior in the visible wavelength range. Such an effect could enhance the local optical density of states, and enhance the emission from the Eu3+ ions. The expected nano-resonator effect that could enhance the radiative transitions in the Eu ions, was not observed This is most likely a result of the non-optimized structure of the surface patterning.

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