Optimized Aluminum Reflector for Enhancement of UVC Cathodoluminescence Based-AlGaN Materials with Carbon Nanotube Field Emitters.

Manoj Kumar Chandra Mohan,Wael Z Tawfik,Naesung Lee,Nakwon Jang,June Key Lee,Sang Kyun Shim

doi:10.3390/molecules26134025

Abstract

The far ultraviolet C (UVC) light sources based on carbon nanotube (CNT) field emitters as excitation sources have become promising light sources for sterilization, disinfection, and water purification. However, the low light extraction efficiency of UVC–CNT light sources still hinders the practical application of these structures. Herein, we report an optimized aluminum (Al) reflector to enhance the light extraction efficiency of UVC–CNT light sources. Optical analysis of UVC-CNT light sources covered by the Al reflectors with various thicknesses ranging from 30 to 150 nm was performed to realize the optimized reflector. The UVC-CNT light sources exhibit the highest light extraction efficiency when the Al reflector layer has an optimized thickness of 100 nm. For comparison, the cathodoluminescence (CL) spectra were recorded for UVC–CNT light sources with and without the optimized Al reflector. The measured light output power and the estimated power efficiency of the UVC–CNT light-source-tube with Al reflector were enhanced by about 27 times over the reference. This enhancement is mainly attributed to the outstanding reflection effect of the Al reflector.

Highlights

Ultraviolet C (UVC) light source tubes based on carbon nanotubes (CNTs) field emitters are promising to replace conventional ultraviolet C (UVC) light-emitting diodes (LEDs) for applications related to air and water sterilization and decontamination [1–3]
To achieve an optimized Al reflector, optical measurements were performed to analyze the effect of the reflector with different thicknesses on the light extraction efficiency of the UVC–CNTs light source tube
The results illustrate that the Al reflector with the optimized thickness of 100 nm can enhance the CL intensity of the AlGaN-based UVC structure, owing to the increase of the light extraction from the top side of the UVCCNTs light source tube

Summary

Introduction

Ultraviolet C (UVC) light source tubes based on carbon nanotubes (CNTs) field emitters are promising to replace conventional UVC light-emitting diodes (LEDs) for applications related to air and water sterilization and decontamination [1–3]. UVC LEDs, which rely on the use of AlGaN nitride epitaxial layers, are still not efficient enough to be considered as possible alternatives on a large industrial scale [4–6] This inefficiency is for different reasons and is related to the quality of the nitride material with high aluminum (Al) composition and/or the technology employed for fabricating the diodes, where low external quantum efficiency is observed. The poor structural quality of the AlGaN epitaxial layers would cause dislocations and create non-radiative defects that destroy the internal quantum efficiency of the LEDs [11–15] These devices currently display low light extraction efficiency and output power [16–19]. Al is an excellent reflector with reflectivity of about ~0.92 in the whole UV spectrum range because of its low refractive index and high extinction coefficient [29] None of these studies have considered the effects of the Al layer’s existence and thickness on the output of UV light source tubes. The vacuum packaging UVC–CNTs light source tube was fabricated in a triode mode structure through the combination of a CNTs field emitter and an AlGaN heterostructure based UVC emission with and without optimum Al cap layer as a CL layer

Methods

Results

Conclusion