Browsing by Author "Lee, Yeeu-Chang"

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Functional imprinting structures on GaN-based light-emitting diodes for light pattern modulation and light extraction efficiency enhancement
(2010-07-01)
Tu, Sheng-Han
;
Wu, Shang-Yen
;
Lee, Yeeu-Chang
;
Pan, Jui-Wen
;
Kuo, Cheng-Huang
In this study, we demonstrated a simple method that can be used to simultaneously modulate the far field pattern and enhance the light extraction of GaN-based light-emitting diodes (LEDs). In this method, microstructures were imprinted on a reliable spin-on-glass surface on top of a transparent conductive layer. The far-field pattern was modulated using microoptical structures, and at the same time, the light extraction was enhanced owing to the small refractive index difference and surface roughness. There was no decrease in the electrical performance of these devices. The peak intensity shifted from 0 to 22A degrees in one-dimensional (1D) asymmetrically blazed periodic structures, and a flattened distribution with a uniform intensity within a span of 110A degrees was observed in two-dimensional (2D) symmetrically periodic structures. This method achieved 13 and 40% light enhancements for 1D and 2D structures, respectively.
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.