High-Power Eu-Doped GaN Red LED Based on a Multilayer Structure Grown at Lower Temperatures by Organometallic Vapor Phas
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High-Power Eu-Doped GaN Red LED Based on a Multilayer Structure Grown at Lower Temperatures by Organometallic Vapor Phase Epitaxy W. Zhu1, B. Mitchell1,2, D. Timmerman3, A. Koizumi1, T. Gregorkiewicz3, Y. Fujiwara1 1
Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka
2
Department of Physics, West Chester University, West Chester, PA, 19383, USA
3
Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098 XH
University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
Amsterdam, The Netherlands ABSTRACT A modification of the growth structure of Eu-doped GaN (GaN:Eu) from a monolayer to a multilayer structure (MLS) consisting of alternating GaN and GaN:Eu, was shown to enhance the emission properties. Similarly, lowering the growth temperature of the GaN:Eu to 960°C nearly doubled the photoluminescence emission intensity, and also enhanced device performance. Hence, to design a higher power GaN:Eu red LED, a multilayer structure consisting of 40 pairs of alternating GaN and GaN:Eu was grown at 960°C. This combination resulted in the fabrication of an LED with a maximum output power of 110 µW, which is 5.8 times more output power per GaN:Eu layer thickness as compared to the best previously reported device. Moreover, it was found that the MLS sample grown at 960°C maintained a high crystal quality with low surface roughness, which enabled an increase in the number of pairs from 40 pairs to 100 pairs. An MLS-LED consisting of 100 pairs of alternating GaN/GaN:Eu layers was successfully fabricated, and had a maximum output power of 375 μW with an external quantum efficiency of 4.6%. These are the highest values reported for this system. INTRODUCTION Wide bandgap III-nitride materials, such as gallium nitride (GaN), have been given considerable attention due to their ability to produce intense emission in the visible and near infrared wavelength regions. Although blue and green light-emitting diodes (LEDs) based on GaN have already been commercialized, nitride-based LEDs in the shorter wavelength region from red to infrared are still premature in terms of intensity. In order to extend the emission wavelength from GaN-based devices, large In compositions are needed to sufficiently reduce the GaN bandgap. However, the low miscibility of In in GaN limits its composition, therefore the growth of InGaN layers with a high In composition and good crystalline quality remains a challenge [1]. Although red LEDs based on InGaN/GaN multiple quantum wells (MQW) have recently been developed [2,3,4], the spectral position and full width at half maximum (FWHM) of the red emission changed with increased injection current. To circumvent the challenges associated with InGaN, Eu-doped GaN (GaN:Eu) based red LEDs have been developed [5,6,7]. These devices exhibit sharp emission lines with a spectral position and FWHM that are not influenced by current injection. These properties make GaN:Eu a promising material for fabricating all GaN-based monolithic active displays, which consist of
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