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Improvement of the light extraction efficiency of GaN-based LEDs using rolled-up nanotube arrays

M. Djavid, X. Liu, and Z. Mi

Open Access Open Access

Abstract

In this paper, we have investigated the effect of rolled-up nanotubes on the light extraction efficiency of GaN-based LEDs using two-dimensional finite element method simulation. The light extraction involves two successive steps, including the coupling from the light source to the tube and the subsequent emission from the tube to the air. Significantly enhanced light extraction efficiency is observed for both TE and TM waves by optimizing the nanotube geometry and dimension as well as the separation between the nanotube and light source. We have further shown that densely packed nanotube arrays can be integrated with GaN-based LEDs to achieve unequivocal improvement of light extraction efficiency over a large surface area. With recent advances in rolled-up micro- and nanotubes, it is expected that this study can offer a potentially flexible, low cost approach to enhance the light extraction of various LED devices.

© 2014 Optical Society of America

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Figures (6)
Fig. 1
Fig. 1 Schematic of the integrated GaN LED and nanotube structure. The nanotube shown here has 1.5 turns and θ is 45°. C1 and C2 denote the integration paths for calculating the light extraction efficiency.

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Fig. 2
Fig. 2 Comparison between the light extraction efficiency of a GaN thin film LED (a) without and (b) with a nanotube for light emission at 526 nm. The nanotube used here has 1.25 turns and the wall thickness is 20 nm.

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Fig. 3
Fig. 3 Light extraction efficiency of (a) TE waves and (b) TM waves vs. the number of turns (N) and rotation angle θ of the nanotube. The wall thickness is 20 nm. The p-GaN layer thickness is d 1 = 120     nm .

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Fig. 4
Fig. 4 Dependence of the light extraction efficiency of TE waves and TM waves on the wall thickness. The p-GaN layer thickness is d 1 = 120     nm . The nanotube parameters are N = 1.25 ,       θ = 0 ° .

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Fig. 5
Fig. 5 Dependence of the light extraction efficiency of TE waves on (a) the depth of the active region and (b) the horizontal position of the point source. Nanotube parameters used are N = 1.6 ,       θ = − 75 ° ,       t = 20     nm . In (a), the light source is positioned right under the nanotube.

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Fig. 6
Fig. 6 (a) Schematic illustration of the integrated nanotube arrays with an LED structure. (b) Comparison between the light extraction efficiency of TE waves for a single nanotube and that for multiple nanotubes for L = 1220 nm. Nanotube parameters include N = 1.6 ,       θ = − 75 ° ,       t = 20 n m .

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Equations (1)

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η= ∫ C 1 S n dl ∮ C 2 S n dl
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