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Materials 2017, 10(4), 432;

Phosphor-Free InGaN White Light Emitting Diodes Using Flip-Chip Technology

Graduate Institute of Electro-Optical Engineering, Chang Gung University, Taoyuan 333, Taiwan
Department of Otolaryngology-Head and Neck Surgery, Chang Gung Memorial Hospital, Taoyuan 333, Taiwan
Department of Materials Engineering, Ming Chi University of Technology, New Taipei City 243, Taiwan
Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan
Department of Physics, University of Central Florida, Orlando, FL 32816, USA
Department of Materials Science and Engineering, University of Central Florida, Orlando, FL 32816, USA
Institute of Physics, Wroclaw University of Technology, 50-370 Wroclaw, Poland
Author to whom correspondence should be addressed.
Received: 9 February 2017 / Revised: 13 April 2017 / Accepted: 17 April 2017 / Published: 20 April 2017
(This article belongs to the Section Structure Analysis and Characterization)
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Monolithic phosphor-free two-color gallium nitride (GaN)-based white light emitting diodes (LED) have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN)/GaN quantum dot and reported LED’s color rendering index (CRI) are still problematic. Here, we use flip-chip technology to fabricate an upside down monolithic two-color phosphor-free LED with four grown layers of high indium quantum dots on top of the three grown layers of lower indium quantum wells separated by a GaN tunneling barrier layer. The photoluminescence (PL) and electroluminescence (EL) spectra of this white LED reveal a broad spectrum ranging from 475 to 675 nm which is close to an ideal white-light source. The corresponding color temperature and color rendering index (CRI) of the fabricated white LED, operated at 350, 500, and 750 mA, are comparable to that of the conventional phosphor-based LEDs. Insights of the epitaxial structure and the transport mechanism were revealed through the TEM and temperature dependent PL and EL measurements. Our results show true potential in the Epi-ready GaN white LEDs for future solid state lighting applications. View Full-Text
Keywords: InGaN/GaN; quantum dot; quantum well; phosphor free; white LED InGaN/GaN; quantum dot; quantum well; phosphor free; white LED

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Li, Y.-C.; Chang, L.-B.; Chen, H.-J.; Yen, C.-Y.; Pan, K.-W.; Huang, B.-R.; Kuo, W.-Y.; Chow, L.; Zhou, D.; Popko, E. Phosphor-Free InGaN White Light Emitting Diodes Using Flip-Chip Technology. Materials 2017, 10, 432.

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