Multi-color broadband visible light source via three-dimensional GaN hexagonal annular microstructures

TL;DR

This paper reports the fabrication of three-dimensional GaN hexagonal annular microstructures with InGaN/GaN MQWs that emit broadband visible light through multi-facet emission, offering a phosphor-free white light source.

Contribution

The study introduces a novel 3D GaN microstructure design enabling multi-color emission from different facets, advancing phosphor-free broadband visible light sources.

Findings

Multi-facet emission enables broadband visible light.

Emission color varies with excitation power density.

High efficiency broadband emission achieved.

Abstract

Broadband visible light emitting, three-dimensional hexagonal annular microstructures with InGaN/GaN multiple quantum wells (MQWs) are fabricated via selective-area epitaxial growth. The single hexagonal annular structure is composed of not only polar facet of (0001) on top surface but also semi-polar facets of {10-11} and {11-22} in inner and outer sidewalls, exhibiting multi-color visible light emission from InGaN/GaN MQWs formed on the different facets. The InGaN MQWs on (0001) facet emits the longer wavelength (green color) due to the larger well thickness and the higher In composition, while those on semi-polar facets of {10-11} and {11-22} had highly-efficient shorter wavelength (violet to blue color) emission caused by smaller well thickness and smaller In composition. By combining the multiple color emission depending on different facets, high efficiency broadband visible light emission could be achieved. The emission color can be changed with excitation power density owing to the built-in electric field on the (0001) facet, which is confirmed by time-resolved luminescence experiments. The hexagonal annular structures can be a critical building block for highly efficient broadband visible light emitting sources, providing a solution to previous problems related to the fabrication issues for phosphor-free white light emitting devices.