We report a dramatic increase in the light emitting efficiency of InGaN/GaN resulting from surface plasmon interaction between the quantum wells and evaporated silver layers, whereas no such enhancement was obtained from gold deposited samples

Mukai, Takashi

Narukawa, Yukio

Niki, Isamu

Okamoto, Koichi

Scherer, Axel

Shvartser, Alexander

Caltech Authors - Main

Surface plasmon enhanced light emitting efficiencies of 
InGaN/GaN quantum wells 
Koichi Okamoto', Isamu Niki", Alexander Shvartser', Yukio Narukawa', Takashi Mukai', 
and Axel SchereS 
'Department ofEIectricu1 Engineering, Calfornia lnslihile of Technology, A4C 136-93, Pasadenu, CA91 I25 
' Nitnde Semiconductor Research Laboratory, Nichia Corporation, 491 Oh, Kaminaka, Anan, Tokushima, 774 -8601, Japan 
Abstract: We report a dramatic increase in the light emitting eficiency of InCaN/CaN resulting 
from surface plasmon interaction between the quantum wells and evaporated silver layers, 
whereas no such enhancement was obtained fmm gold deposited samples. 
02000 Optical Society of America 
OCIS codes: (000.0000) General 
Since 1993, InGaN light emitting diodes have been commercialized as blue light souI'ces [l], but their original 
promise as solid state replacements for light bulbs has so far been delayed as their light emission efficiencies have so 
far been limited. Recently, surface plasmon (SP) has received much attention to enhance the light emission of light 
emitting diodes (LEDs) 121. Although coupling of spontaneous emission from InCaN into SP modes has been 
observed, light has not yet been efficiently extracted from plasmon structures at visible wavelengths [3-41. Here we 
first report large photoluminescence (PL) enhancements from InGaN/GaN QW material coated with metal layers. 
By polishing the bottom surface of grown InGaN samples, QW emission can be photoexcited and measured through 
the back of the substrate. 
InGaN ,QW were grown by MOCVD. 10 nm, 40 nm, and 150 nm thick GaN spacers were grown onto these 
QWs, and 50 nm thick Ag, Al, or Au layers were evaporated on top of the wafer surfaces. PL measurements were 
performed by exdting the QW with a 406nm diode laser from the back of the substrates, and collecting 
luminescence with a multichannel spectrometer. 
Fig. 1 shows PL spectrum from InCaN/CaN QW sepamted from Ag, AI and Au layer by a l O n m  GaN spacer. 
The PL peak of the uncoated wafer at 470 nm is normalized to 1. 14-fold peak intensity and 17-fold integrated 
intensity enhancements were observed from the Ag coated emitter. Also, 8-fold peak intensity and 6-fold integrated 
intensity enlmcemenis are obtained from A1 coated sample, whereas PL is not increased after Au coating. PL 
intensities of A1 and Ag coated samples were also found to strongly depend on the distance between QWs and the 
metal. These ~ s u l t 3  suggest that the emission enhancement after coating with Ag and A1 can be attributed to strong 
interaction with SP. 
1 5 , ,  , I , ,  , , , I ,  
440 460 480 500 520 
10-1 ' ' ' ' ' I ' I ' ' 
0 10 20 30 40 50 
Wavelength (nm) 1 OOO/T (K-I) 
Fig. 1 PL spectra of InGaN/GaN with Ag, AI and Au layers Fig. 2 Temperature dependence of PL intensities 
SP-QW coupling should increases internal quantum efficiency ( v , ~ )  by enhancing the spontaneous 
recombination rate. Fig. 2 shows the linear and Arrhenius plots of the integrated PL intensities from InGaN QWs 
separated from Ag and AI films by l O n m  spacers, and compares these to uncoated samples. qylt values from 
uncoated QWs were estimated as 6 % at room temperature by assuming qyd -100% at 4.2K. These qmt values 
increased 6.8 times (to 41%) after Ag coating and 3 times (to 18%) after A1 coating, explainable by spontaneous 
recombination rate enhancements through SP coupling. 
SP coupling is one of the most interesting methods for developing efficient LEDs, as the metal can be used both 
as electrical contact and for exciting plasmons. 
[l]  S. Nakamura, T. Mukai and M. Senoh, Appl. P 
[2] J. Vuckovic, M. Loncar, and A. Scherer, IEEE 
131 I. Gontijo, M. Borodisky, E. Yablonvitch, S. Keller, U. K. Mishra, and S. P. DenBaars, Phys. Rev. B, 60, 11564 (1999). 
[4] A. Neogi, C.-W. Lee, H. 0. Eventt, T Kuroda, A. Tackeuchi, and E. Yablonvitch, Phys. Rev. B, 66, 153305 (2002). 


Surface plasmon enhanced light emitting efficiencies of InGaN/GaN quantum wells

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Surface plasmon enhanced light emitting efficiencies of InGaN/GaN quantum wells

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