UVB LEDs Grown by Molecular Beam Epitaxy Using AlGaN Quantum Dots

Julien Brault,Mathieu Leroux,Bernard Gil,Sébastien Chenot,Samuel Matta,Pierre Valvin,Thi Huong Ngo,Mohamed Al Khalfioui

doi:10.3390/cryst10121097

Julien Brault, Mathieu Leroux + Show 6 more

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https://doi.org/10.3390/cryst10121097

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Abstract

AlGaN based light emitting diodes (LEDs) will play a key role for the development of applications in the ultra-violet (UV). In the UVB region (280–320 nm), phototherapy and plant lighting are among the targeted uses. However, UVB LED performances still need to be improved to reach commercial markets. In particular, the design and the fabrication process of the active region are central elements that affect the LED internal quantum efficiency (IQE). We propose the use of nanometer-sized epitaxial islands (i.e., so called quantum dots (QDs)) to enhance the carrier localization and improve the IQE of molecular beam epitaxy (MBE) grown UVB LEDs using sapphire substrates with thin sub-µm AlN templates. Taking advantage of the epitaxial stress, AlGaN QDs with nanometer-sized (≤10 nm) lateral and vertical dimensions have been grown by MBE. The IQE of the QDs has been deduced from temperature dependent and time resolved photoluminescence measurements. Room temperature IQE values around 5 to 10% have been found in the 290–320 nm range. QD-based UVB LEDs were then fabricated and characterized by electrical and electroluminescence measurements. On-wafer measurements showed optical powers up to 0.25 mW with external quantum efficiency (EQE) values around 0.1% in the 305–320 nm range.

Highlights

Nitride based light emitting diodes (LEDs) can emit in the ultra-violet (UV) range from the near UV [1], which is a part of the UVA region (400 nm ≤ λUVA ≤ 320 nm), down to the UVC region (280 nm ≤ λUVC ≤ 100 nm) reaching a minimum wavelength emission of 210 nm achieved by using an AlN p-i-n junction [2]
The second part is dedicated to the investigation of the quantum dots (QDs)-based LEDs including PL, I–V, and EL measurements
Al0.2 Ga0.8 N QD-based LEDs emitting in the UVB range have been fabricated by molecular beam epitaxy (MBE) using two different designs for the active region: 3 QD planes separated by 10-nm thick barrier layers (LED-A)

Summary

Introduction

Nitride based light emitting diodes (LEDs) can emit in the ultra-violet (UV) range from the near UV [1], which is a part of the UVA region (400 nm ≤ λUVA ≤ 320 nm), down to the UVC region (280 nm ≤ λUVC ≤ 100 nm) reaching a minimum wavelength emission of 210 nm achieved by using an AlN p-i-n junction [2]. Compared to the other existing UV sources, LEDs offer strong advantages such as low power consumption, compactness and long lifetimes. They are an environmentally-friendly solution to the commonly used mercury (Hg) lamps, which bring toxicity and recycling issues. The UVC spectral region is targeting strategic applications for sterilization, water purification and surface disinfection, by inducing bacteria cell inactivation [5]. Another region of interest is the UVB for medical and environmental applications, such as skin treatment and plant growth [4].

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