Browsing by Author "Chang, Yung-Yuan"

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High-efficiency InGaN-based LEDs grown on patterned sapphire substrates using nanoimprinting technology
(2013-05-01)
Lee, Yeeu-Chang
;
Yeh, Shiang-Chih
;
Chou, Yen-Yu
;
Tsai, Pei-Jung
;
Pan, Jui-Wen
This study employed roller imprint lithography and dry etching to fabricate patterned sapphire substrates (PSSs) of convex-shape with features of various heights. A soft polymer, polydimethylsiloxane (PDMS), was used as a mold to duplicate the pattern of a hard silicon template. The imprinted material was spin deposited onto a PDMS mold and transferred to the sapphire substrate using roller imprinting equipment. Inductive coupled plasma (ICP) etching was then used to fabricate the PSS. After epitaxial growth and chip processing, the current-voltage characteristics and light output of various LEDs were measured. The results demonstrate that the PSS process did not detract from the electrical properties of the LEDs; in fact, the output power of the proposed PSS LEDs was 25-30% greater than that of conventional LEDs. Simulation results show that PSS LEDs with structures of various heights would enhance optical efficiency in a manner similar to that demonstrated in these experiments. (C) 2013 Elsevier B.V. All rights reserved.
Light extraction efficiency analysis of GaN-based light-emitting diodes with nanopatterned sapphire substrates
(2013-03-01)
Pan, Jui-Wen
;
Tsai, Pei-Jung
;
Chang, Kao-Der
;
Chang, Yung-Yuan
;
光電系統研究所
In this paper, we propose a method to analyze the light extraction efficiency (LEE) enhancement of a nanopatterned sapphire substrates (NPSS) light-emitting diode (LED) by comparing wave optics software with ray optics software. Finite-difference time-domain (FDTD) simulations represent the wave optics software and Light Tools (LTs) simulations represent the ray optics software. First, we find the trends of and an optimal solution for the LEE enhancement when the 2D-FDTD simulations are used to save on simulation time and computational memory. The rigorous coupled-wave analysis method is utilized to explain the trend we get from the 2D-FDTD algorithm. The optimal solution is then applied in 3D-FDTD and LTs simulations. The results are similar and the difference in LEE enhancement between the two simulations does not exceed 8.5% in the small LED chip area. More than 104 times computational memory is saved during the LTs simulation in comparison to the 3D-FDTD simulation. Moreover, LEE enhancement from the side of the LED can be obtained in the LTs simulation. An actual-size NPSS LED is simulated using the LTs. The results show a more than 307% improvement in the total LEE enhancement of the NPSS LED with the optimal solution compared to the conventional LED. (C) 2013 Optical Society of America