Abstract

Analysis of the various light extraction efficiency enhancement mechanisms for the GaN-based light emitting diodes (LEDs) was investigated. Experiments utilized the imprinting technique to fabricate pyramid and inverted pyramid microstructures. Roughness treatment was then integrated with these imprinting structures on patterned sapphire substrate (PSS) LEDs. An approximate 33% improvement in light output power was obtained using the pyramid profile when compared with the planar LED. This was nearly 15% higher than that of the inverted pyramid profile. The roughness effect provided an approximate 5% efficiency enhancement. The total light enhanced efficiency increased to 85.9% by integrating the imprinting pyramid structure, PSS, and surface roughness.

© 2010 OSA

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Figures (8)

Fig. 1
Fig. 1

Process flow to prepare a microstructure with a roughness effect on PSS LEDs.

Fig. 2
Fig. 2

(a) SEM microphotograph of silicon concave mold and (b) SEM microphotograph of PDMS convex mold.

Fig. 3
Fig. 3

(a) SEM microphotograph of imprinting pyramids, and (b) SEM microphotograph of imprinting inverted pyramid.

Fig. 4
Fig. 4

(a) SEM microphotograph of the imprinting inverted pyramid before and after roughness treatment. (b) SEM microphotograph of the imprinting pyramid before and after roughness treatment.

Fig. 5
Fig. 5

Light output power versus input current for the C group of Table 1.

Fig. 6
Fig. 6

(a) Possible photon paths for planar PMMA on the LED. (b) Possible photon paths for roughened PMMA on the LED. (c) Possible photon paths for pyramid PMMA on the LED. (d) Comparison of possible photon paths for pyramid and inverted pyramid.

Fig. 7
Fig. 7

Light output power versus input current for P group of Table 2.

Fig. 8
Fig. 8

SEM microphotograph of the pyramid arrays with small slanted angle.

Tables (4)

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Table 1 Overview of the planar PMMA, imprinting PMMA and roughness treatment for conventional LEDs

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Table 2 Overview of the planar PMMA, imprinting PMMA and roughness treatment for PSS LEDs

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Table 3 Light output power and relative enhanced efficiency of C group LEDs

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Table 4 Light output power and relative enhanced efficiency of P group LEDs

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