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Appl. Sci. 2017, 7(6), 506; doi:10.3390/app7060506

Improved Performance of High-Voltage Vertical GaN LEDs via Modification of Micro-Cell Geometry

1
Department of Materials Science and Engineering, National Chung Hsing University, Taichung 40227, Taiwan
2
Department of Materials Science and Engineering, Da-Yeh University, Changhua 51591, Taiwan
3
Institute of Electronics, National Chiao Tung University, Hsinchu 30010, Taiwan
*
Author to whom correspondence should be addressed.
Academic Editor: Paolo Minzioni
Received: 24 March 2017 / Revised: 7 May 2017 / Accepted: 9 May 2017 / Published: 24 May 2017
(This article belongs to the Section Optics and Lasers)
View Full-Text   |   Download PDF [2503 KB, uploaded 24 May 2017]   |  

Abstract

Vertical-type high-voltage light-emitting diodes (HV-LEDs) with 2 × 2 micro-cells were fabricated on Cu substrates, and the micro-cell geometry was modified to enhance the optoelectronic performance. The current spreading in micro-cell is most dominantly affected by the distance between electrode and edge of chip. When square cells were combined in a HV-LED, the device performance was poor due to an obvious current-crowding phenomenon that occurred near the electrodes. This was attributed that the electrodes in these four square micro-cells were all far away from the edges, resulting in the severe current-crowding phenomenon. On the contrary, as the HV-LED was prepared with four rectangle, triangle, or L-shaped micro-cells, the electrodes were close to the edges of micro-cells and the current spreading effect can be easily improved. Although a HV-LED connected with L-shaped cells possessed a better current spreading effect and a lower surface temperature, the light extraction was relatively low because of an electrode-shading loss effect. When triangular cells were used to prepare the HV-LED, the device achieved a superior optoelectronic performance compared with that of other cells because of a lower current-crowding effect and a more uniform light emission. After an epoxy package process, a lower forward voltage of 14.9 V and a higher output power of 353.2 mW were obtained using this HV-LED at an injection current of 80 mA. Additionally, the wall-plug efficiencies of this device at 20 and 80 mA were 41.1% and 29.7%, respectively. The results confirm that the design of triangular cell is beneficial for enhancing the optoelectronic performance of HV-LEDs. Furthermore, the fabrication processes of vertical LEDs have high potential for HV-LED applications. View Full-Text
Keywords: vertical light emitting diodes; high-voltage light emitting diodes; micro-cell geometry; current crowding effect; spatial distribution image vertical light emitting diodes; high-voltage light emitting diodes; micro-cell geometry; current crowding effect; spatial distribution image
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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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MDPI and ACS Style

Wu, P.-C.; Ou, S.-L.; Horng, R.-H.; Wuu, D.-S. Improved Performance of High-Voltage Vertical GaN LEDs via Modification of Micro-Cell Geometry. Appl. Sci. 2017, 7, 506.

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