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Analysis of light extraction efficiency enhancement for thin-film-flip-chip InGaN quantum wells light-emitting diodes with GaN micro-domes

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Abstract

The enhancement of light extraction efficiency for thin-film flip-chip (TFFC) InGaN quantum wells (QWs) light-emitting diodes (LEDs) with GaN micro-domes on n-GaN layer was studied. The light extraction efficiency of TFFC InGaN QWs LEDs with GaN micro-domes were calculated and compared to that of the conventional TFFC InGaN QWs LEDs with flat surface. The three dimensional finite difference time domain (3D-FDTD) method was used to calculate the light extraction efficiency for the InGaN QWs LEDs emitting at 460nm and 550 nm, respectively. The effects of the GaN micro-dome feature size and the p-GaN layer thickness on the light extraction efficiency were studied systematically. Studies indicate that the p-GaN layer thickness is critical for optimizing the TFFC LED light extraction efficiency. Significant enhancement of the light extraction efficiency (2.5-2.7 times for λpeak = 460nm and 2.7-2.8 times for λpeak = 550nm) is achievable from TFFC InGaN QWs LEDs with optimized GaN micro-dome diameter and height.

©2012 Optical Society of America

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Figures (8)

Fig. 1
Fig. 1 2D schematics of the thin film flip-chip (TFFC) InGaN QWs LEDs with (a) flat surface and (b) GaN micro-domes.
Fig. 2
Fig. 2 Yee’s mesh cell: Maxwell’s equations are solved discretely in unit of Yee’s mesh cell.
Fig. 3
Fig. 3 Spontaneous emission spectra (TE component and TM component (x50)) for InxGa1-xN QWs LEDs with x = 0.1, 0.2, 0.25 and 0.3.
Fig. 4
Fig. 4 Schematic of TFFC InGaN QWs LED with interference between emission of QWs and from bottom mirror.
Fig. 5
Fig. 5 Light extraction efficiency for the conventional TFFC InGaN QWs LEDs at wavelength (a) λpeak = 460nm and (b) λpeak = 550nm with flat surface as a function of the p-GaN layer thickness. N-GaN thickness is 2.5μm. Dash line and solid dots represent the theoretical fitting curve and the FDTD calculation results, respectively.
Fig. 6
Fig. 6 Light extraction efficiency enhancement of TE polarized spontaneous emission component for TFFC InGaN QWs LEDs with optimized p-GaN thickness (195nm for λpeak = 460nm, 230nm for λpeak = 550nm as a function of GaN micro-hemisphere diameter (D).
Fig. 7
Fig. 7 (a) Geometric structure of the general micro-dome structure on n-GaN emission surface of TFFC InGaN QWs LED with diameter D and height h; (b) light extraction efficiency at λpeak = 460nm from InGaN QWs TFFC LED with micro-dome structures as a function of micro-dome height h for diameters D = 500nm, D = 1000nm and D = 1500nm.
Fig. 8
Fig. 8 Light extraction efficiency for the conventional TFFC InGaN QWs LEDs (λpeak = 460nm) with flat surface and with GaN micro-domes as a function of the p-GaN layer thickness assuming the ambient medium is (a) air (n = 1), and (b) epoxy resin (n~1.5). Dash lines and solid dots represent the theoretical fitting curves and the FDTD calculation results, respectively.

Equations (6)

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E z n+1 =( 1σΔt/2ε 1+σΔt/2ε ) E x n +( 2Δt/Δs 2ε+σΔt )( Δ H y n+ 1 2 +Δ H x n+ 1 2 )
Ε( ω )= 1 2 real( P( ω ) )d S
P( ω )=n( ω ) ε 0 μ 0 | E ( ω ) | 2
E 2 ( ω )= E 0 2 (ω) | 1±r e 2iϕ(ω) | 2 = E 0 2 (ω)( 1+ r 2 ±2rcos2ϕ(ω) )
2ϕ=2ktcosθ
t(ω)= mλ 2n(ω)
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