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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 7 — Apr. 8, 2013
  • pp: 8062–8068
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Improved performance of GaN-based vertical light emitting diodes with conducting and transparent single-walled carbon nanotube networks

Su Jin Kim, Kyeong Heon Kim, and Tae Geun Kim  »View Author Affiliations


Optics Express, Vol. 21, Issue 7, pp. 8062-8068 (2013)
http://dx.doi.org/10.1364/OE.21.008062


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Abstract

In this study, reduced forward voltage and improved light output power of GaN-based vertical light-emitting diodes (VLEDs) incorporating single-walled carbon nanotube (SWNT)-networks is reported. The SWNT-networks were directly formed on a roughened (textured) n-GaN surface via a solution-processed dip-coating method. The surface-roughened VLEDs with the proposed SWNT-networks had a forward voltage of 3.84 V at 350 mA, lower than that of the surface-roughened VLEDs, and exhibited an increase in light output power by 12.9% at 350 mA compared to the surface-roughened VLEDs. These improved electrical and optical properties could be attributed to the SWNT-networks put on the roughened n-GaN surface, which increase the lateral current transport and create scattering of light through the formation of additional roughness.

© 2013 OSA

1. Introduction

GaN-based vertical light-emitting emitting diodes (VLEDs) have been suggested as a solution for high-efficiency and high-power applications in solid-state lighting. VLEDs provide many advantages compared to conventional LEDs, including larger emitting area, better current spreading, excellent heat dissipation and simple packaging [1

1. C. F. Chu, C. C. Cheng, W. H. Liu, J. Y. Chu, F. H. Fan, H. C. Cheng, T. Doan, and C. A. Tran, “High brightness GaN vertical light-emitting diodes on metal alloy for general lighting application,” Proc. IEEE 98(7), 1197–1207 (2010). [CrossRef]

]. However, the light extraction efficiency is basically limited by total internal reflection due to the large difference in the refractive index between GaN (n ~2.5) and air (n = 1.0). As a result, only a small fraction of photons generated in the active region can escape into free surfaces [2

2. T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855 (2004). [CrossRef]

]. To increase the light extraction, various surface texturing methods such as photoelectrochemical etching [2

2. T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855 (2004). [CrossRef]

], nanoimprint lithography [3

3. H. K. Cho, J. Jang, J. H. Choi, J. Choi, J. W. Kim, J. S. Lee, B. S. Lee, Y. H. Choe, K. D. Lee, S. H. Kim, K. Lee, S. K. Kim, and Y. H. Lee, “Light extraction enhancement from nano-imprinted photonic crystal GaN-based blue light-emitting diodes,” Opt. Express 14(19), 8654–8660 (2006). [CrossRef] [PubMed]

], nanosphere lithography [4

4. H.-M. An, J. I. Sim, K. S. Shin, Y. M. Sung, and T. G. Kim, “Increased light extraction from vertical GaN light-emitting diodes with ordered, cone-shaped deep-pillar nanostructures,” IEEE J. Quantum Electron. 48(7), 891–896 (2012). [CrossRef]

], electron beam lithography [5

5. T. N. Oder, K. H. Kim, J. Y. Lin, and H. X. Jiang, “III-nitride blue and ultraviolet photonic crystal light emitting diodes,” Appl. Phys. Lett. 84(4), 466–468 (2004). [CrossRef]

] and laser interference lithography have been applied to n-GaN surface of VLEDs [6

6. Y. C. Shin, D. H. Kim, D. J. Chae, J. W. Yang, J. I. Shim, J. M. Park, K.-M. Ho, K. Constant, H. Y. Ryu, and T. G. Kim, “Effects of nanometer-scale photonic crystal structures on the light extraction from GaN light emitting diodes,” IEEE J. Quantum Electron. 46(9), 1375–1380 (2010). [CrossRef]

]. However, these patterning methods often involve dry-etching processes, which can degrade the electrical properties due to plasma-induced damage, leading to the increase of leakage currents in GaN in addition to the increase of light extraction [7

7. R. H. Horng, C. C. Yang, J. Y. Wu, S. H. Huang, C. E. Lee, and D. S. Wuu, “GaN-based light-emitting diodes with indium tin oxide texturing window layers using natural lithography,” Appl. Phys. Lett. 86(22), 221101 (2005). [CrossRef]

, 8

8. X. A. Cao, H. Piao, J. Li, J. Y. Lin, and H. X. Jiang, “Surface chemical and electronic properties of plasma-treated n-type Al0.5Ga0.5N,” Phys. Status Solidi 204(10), 3410–3416 (2007) (a). [CrossRef]

]. Besides, although VLEDs have shown higher light output power and lower forward voltage drop compared with conventional LEDs, the light emission is basically hindered by current accumulation and thereby light absorption below opaque n-type electrodes in VLEDs. Therefore, some efforts have been made to improve the lateral current spreading using insulating SiO2 current-blocking layers and transparent indium-zinc-oxide layers [9

9. K. M. Uang, S. J. Wang, T.-M. Chen, W.-C. Lee, S.-L. Chen, Y.-Y. Wang, and H. Kuan, “Enhanced Performance of Vertical GaN-Based Light-Emitting Diodes with a Current-Blocking Layer and Electroplated Nickel Substrate,” Jpn. J. Appl. Phys. 48(10), 102101 (2009). [CrossRef]

, 10

10. S.-J. Wang, S.-L. Chen, K.-M. Uang, W.-C. Lee, T.-M. Chen, C.-H. Chen, and B.-W. Liou, “The Use of Transparent Conducting Indium–Zinc Oxide Film as a Current Spreading Layer for Vertical-Structured High-Power GaN-Based Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 18(10), 1146–1148 (2006). [CrossRef]

].

Recently, single-walled carbon nanotubes (SWNTs) have attracted considerable attention as transparent conducting films because they have excellent electrical properties with high transparency [11

11. J. P. Novak, M. D. Lay, F. K. Perkins, and E. S. Snow, “Macroelectronic applications of carbon nanotube networks,” Solid-State Electron. 48(10–11), 1753–1756 (2004). [CrossRef]

, 12

12. L. Hu, D. S. Hecht, and G. Gruner, “Percolation in Transparent and Conducting Carbon Nanotube Networks,” Nano Lett. 4(12), 2513–2517 (2004). [CrossRef]

]. Many attempts have been taken to assemble SWNT films on substrates such as using spray-coating [13

13. R. C. Tenent, T. M. Barnes, J. D. Bergeson, A. J. Ferguson, B. To, L. M. Gedvilas, M. J. Heben, and J. L. Blackburn, “Ultrasmooth, Large‐Area, High‐Uniformity, Conductive Transparent Single‐Walled‐Carbon‐Nanotube Films for Photovoltaics Produced by Ultrasonic Spraying,” Adv. Mater. 21(31), 3210–3216 (2009). [CrossRef]

], spin coating [14

14. M. A. Meitl, Y. Zhou, A. Gaur, S. Jeon, M. L. Usrey, M. S. Strano, and J. Rogers, “Solution Casting and Transfer Printing Single-Walled Carbon Nanotube Films,” Nano Lett. 4(9), 1643–1647 (2004). [CrossRef]

], the combination of vacuum filtration and transfer printing [15

15. M. W. Rowell, M. A. Topinka, M. D. McGehee, H. J. Prall, G. Dennler, N. S. Sariciftci, L. B. Hu, and G. Gruner, “Organic solar cells with carbon nanotube network electrodes,” Appl. Phys. Lett. 88(23), 233506 (2006). [CrossRef]

], drop-casting from solvents [16

16. T. V. Sreekumar, T. Liu, S. Kumar, L. M. Ericson, R. H. Hauge, and R. E. Smalley, “Single-Wall Carbon Nanotube Films,” Chem. Mater. 15(1), 175–178 (2003). [CrossRef]

], magnetic force [17

17. D. P. Long, J. L. Lazorcik, and R. Shashidhar, “Magnetically Directed Self-Assembly of Carbon Nanotube Devices,” Adv. Mater. 16(9–10), 815–819 (2004).

], the dielectrophoretic force [18

18. S. Blatt, F. Hennrich, H. V. Löhneysen, M. M. Kappes, A. Vijayaraghavan, and R. Krupke, “Influence of Structural and Dielectric Anisotropy on the Dielectrophoresis of Single-Walled Carbon Nanotubes,” Nano Lett. 7(7), 1960–1966 (2007). [CrossRef] [PubMed]

], and quasi-Langmuir-Blodgett deposition [19

19. N. P. Armitage, J. C. P. Gabriel, and G. Gruner, “Quasi-Langmuir–Blodgett thin film deposition of carbon nanotubes,” J. Appl. Phys. 95(6), 3228 (2004). [CrossRef]

]. Among these methods, we used a simple and reproducible dip coating method to fabricate selectively self-assembled SWNT-networks without additional chemical processes [20

20. K. H. Kim, C. W. Jang, T. G. Kim, S. Lee, S. H. Kim, and Y. T. Byun, “Processing Technique for Single-Walled Carbon Nanotube-Based Sensor Arrays,” J. Nanosci. Nanotechnol. 12(2), 1251–1255 (2012). [CrossRef] [PubMed]

, 21

21. K. H. Kim, T. G. Kim, S. Lee, Y. M. Jhon, S. H. Kim, and Y. T. Byun, “Simple Assembling Technique of Single-Walled Carbon Nanotubed Using Only Photolithography,” J. Korean Phys. Soc. 58(5), 1380–1383 (2011).

]. In this work, in order to further enhance the lateral current spreading and external quantum efficiency, VLEDs with SWNT-networks formed on roughened n-GaN as a transparent current conducting layer are proposed and fabricated. Then, the effect of the SWNT-network layer on the electrical and optical properties of VLEDs is presented.

2. Experiment

Figure 1
Fig. 1 The schematic illustration of GaN-based vertical LEDs with surface roughened by wet etching and coated with ultra-thin SWNT-networks.
shows schematic drawings of the surface textured GaN-based VLED with surface-mounted SWNT-networks, and the light scattering used in this study. The GaN-based LED samples used in this experiment were grown by metal organic chemical vapor deposition on c-plane sapphire substrates. The GaN LED epilayers consist of a 2-μm-thick undoped GaN layer, a 3.5-μm-thick n-GaN layer, five InGaN/GaN multi-quantum well (MQW) layers, and a 150-nm-thick p-GaN layer. The Ag-based reflective p-Ohmic contact was deposited on the LED epilayers, which was then bonded to silicon substrate using Au-Sn metallizations at 300 °C for 20 min. After that, the sapphire was separated from the LED structure by a laser lift-off (LLO) process with a KrF excimer laser (248 nm). After the lift-off process, the samples were treated by HCl solution (HCl: DI = 1: 1) for 2 min to remove the residual Ga droplets on the exposed undoped GaN surfaces. Inductively coupled plasma (ICP) etching was then used to dry-etch the undoped GaN layer in order to expose the n-GaN surface. BCl3 (30 sccm) and Cl2 (15sccm) were used as the etching gas with an ICP power of 500 W and an RF (radio frequency) power of 100 W. The process pressure was 5 × 10−3 torr.

The randomly surface roughening of n-GaN was then performed by 6-mol KOH-based wet chemical etching. To prepare SWNTs solution (0.3 mg/ml in 1,2-dichlorobenzene), commercially available purified SWNT powders (super pure grade purchased from Unidym, Inc.), synthesized by high-pressure carbon monoxide (HiPco) processing at high temperatures, were immersed in 1,2-dichlorobenzene solvent without surfactants, which were then sonicated for 3 h to obtain the uniform SWNTs dispersion. Afterwards, the wafer-scale VLEDs were dipped and suspended in the SWNTs-dispersed solution for 3 min to adsorb the SWNT-networks onto the roughened surface of the VLEDs, and then rinsed multiple times using 1,2-dichlorobenzene and blown dry with pure nitrogen gas. The same process was repeated four times to organize compact wiring between the SWNTs and the rough n-GaN surface. The VLEDs with SWNT-networks were subsequently dried over a hotplate at 120 °C for 30 min to vaporize remaining solvent and to attain strong adhesion between SWNTs and rough n-GaN surface. The following standard photolithography and ICP-RIE processes defined isolated mesa structures. Finally, Cr/Au was deposited on the SWNT-networks/n-GaN surface as an n-electrode by electron-beam evaporation. Because of good adhesion between SWNT-networks and n-GaN surface, peeling off was not observed even after photolithography and metal lift-off process. The chip area of the LED was 1 mm × 1 mm. For comparison, surface-roughened VLED without SWNT-networks was also prepared using the same LED epitaxial wafer under the same fabrication process. The transmittance of SWNT-networks was measured using a UV/visible spectrophotometer system. The current-voltage (I-V) characteristics of the devices were measured using a Keithley 4200 analyzer. The light output power and electroluminescence (EL) were measured for full-structure LED chips using wafer-level LED measurement systems. The current-spreading images of VLEDs were elucidated by a photoemission microscope.

3. Results and discussion

Figure 3
Fig. 3 The optical transmittance spectra of samples prepared with SWNT-networks on quartz substrates with different dipping number.
shows optical transmittance spectra of the SWNT-networks as a function of wavelength with different dipping number. The transmittance values of the SWNT-networks after 1, 2, 3, and 4 times dipping were 97.7, 97, 96.6 and 95.5% at 460 nm wavelength, respectively, which indicates that the transmittance decreases as the density of the SWNT-networks increases. As the dipping number is increased, the films became less transparent due to the increase of light absorption in SWNTs. Therefore, it is important for the SWNT-networks to be well interconnected on the GaN surface for maximizing the electrical conducting path, while maintaining optical transmittance without significant losses. Our devices were fabricated under these conditions (4 times).

Figure 4(a)
Fig. 4 (a) The current versus forward voltage (I−V) curve characteristics, in which the inset shows the dynamic resistance characteristic curves, and (b) the current versus light output power (L-I) curve characteristics measured from the surface-roughened VLEDs and the proposed VLEDs with the SWNT-networks. Inset shows the EL spectra taken at 200 mA.
shows the comparison of I–V characteristic curves measured for the surface-roughened VLEDs and the proposed VLEDs with the SWNT-networks. The experimental results show that the forward voltages of the surface-roughened VLEDs with and without the SWNT-networks at 350 mA were 3.99 and 3.84 V, respectively. A forward voltage drop of 0.15 V is attributed to the uniform current injection at the entire n-GaN surface via the SWNT-networks. The interconnecting SWNT-network layers provide tunnels for the electrons to transport in the lateral direction [22

22. G. Xiao, Y. Tao, J. Lu, and Z. Zhang, “Highly conductive and transparent carbon nanotube composite thin films deposited on polyethylene terephthalate solution dipping,” Thin Solid Films 518(10), 2822–2824 (2010). [CrossRef]

], which improves the current spreading in the VLEDs. The improved lateral current spreading then allows uniform current injection from the entire n-GaN surface, eventually decreasing the forward voltage and increasing the light output power. The inset of Fig. 4(a) shows dynamic resistance characteristic curves of the two samples, in which we found that the dynamic resistance of the VLED with SWNTs is slightly lower than that of the VLED without SWNTs for a voltage of more than 2.5 V.

In order to examine the effect of SWNT-networks on the current spreading and light extraction efficiency in VLEDs, the luminescence distributions and the light intensity profiles were measured at 20 mA to obtain clear images of the current spreading effects and the luminescence distribution. The light emission intensities were indicated by the color bar as shown in the right-hand side of luminescence distribution images. In Fig. 5(a)
Fig. 5 The luminescence distribution images and (b) the light intensity profiles along the dotted horizontal line measured from the surface-roughened VLEDs and the proposed VLEDs with the SWNT-networks.
, it is found that the light emission is more uniformly distributed in the proposed VLEDs with the SWNT-networks rather than the surface-roughened VLEDs. This improvement may be due to the interconnecting SWNT-networks, which can increase the current path and hence the current spreading over the entire area, and eventually, lead to more uniform light emission patterns across the electrode pads. Figure 5(b) shows the light intensity profiles measured along the dotted lines in Fig. 5(a). Compared with the surface-roughened VLEDs, more uniform and enhanced light output intensity is observed from the proposed VLEDs with the SWNT-networks. Consequently, the increase of the current spreading in addition to the increase of the light extraction discussed in Fig. 5, via SWNT-networks, are attributed to the enhanced light output power in this work. These results are also reasonably consistent with the data obtained in Figs. 4 and 5.

4. Conclusion

We proposed an SWNT-network as a transparent current conducting layer in VLEDs, which demonstrated improved electrical and optical characteristics. Under 350-mA current injection, it was shown that the VLEDs with the proposed SWNT-network exhibited an operating voltage reduction of 0.15 V and light output power increase of 12.9% compared with VLEDs without the SWNT-network. These improved electrical and optical properties can be attributed to the SWNT-networks on the roughened n-GaN surface, which can significantly enhance the lateral current transport and generate scattering and diffraction of light between the sidewall of the roughened n-GaN surface and the SWNT-network layer.

Acknowledgment

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (No. 2011-0028769).

References and links

1.

C. F. Chu, C. C. Cheng, W. H. Liu, J. Y. Chu, F. H. Fan, H. C. Cheng, T. Doan, and C. A. Tran, “High brightness GaN vertical light-emitting diodes on metal alloy for general lighting application,” Proc. IEEE 98(7), 1197–1207 (2010). [CrossRef]

2.

T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett. 84(6), 855 (2004). [CrossRef]

3.

H. K. Cho, J. Jang, J. H. Choi, J. Choi, J. W. Kim, J. S. Lee, B. S. Lee, Y. H. Choe, K. D. Lee, S. H. Kim, K. Lee, S. K. Kim, and Y. H. Lee, “Light extraction enhancement from nano-imprinted photonic crystal GaN-based blue light-emitting diodes,” Opt. Express 14(19), 8654–8660 (2006). [CrossRef] [PubMed]

4.

H.-M. An, J. I. Sim, K. S. Shin, Y. M. Sung, and T. G. Kim, “Increased light extraction from vertical GaN light-emitting diodes with ordered, cone-shaped deep-pillar nanostructures,” IEEE J. Quantum Electron. 48(7), 891–896 (2012). [CrossRef]

5.

T. N. Oder, K. H. Kim, J. Y. Lin, and H. X. Jiang, “III-nitride blue and ultraviolet photonic crystal light emitting diodes,” Appl. Phys. Lett. 84(4), 466–468 (2004). [CrossRef]

6.

Y. C. Shin, D. H. Kim, D. J. Chae, J. W. Yang, J. I. Shim, J. M. Park, K.-M. Ho, K. Constant, H. Y. Ryu, and T. G. Kim, “Effects of nanometer-scale photonic crystal structures on the light extraction from GaN light emitting diodes,” IEEE J. Quantum Electron. 46(9), 1375–1380 (2010). [CrossRef]

7.

R. H. Horng, C. C. Yang, J. Y. Wu, S. H. Huang, C. E. Lee, and D. S. Wuu, “GaN-based light-emitting diodes with indium tin oxide texturing window layers using natural lithography,” Appl. Phys. Lett. 86(22), 221101 (2005). [CrossRef]

8.

X. A. Cao, H. Piao, J. Li, J. Y. Lin, and H. X. Jiang, “Surface chemical and electronic properties of plasma-treated n-type Al0.5Ga0.5N,” Phys. Status Solidi 204(10), 3410–3416 (2007) (a). [CrossRef]

9.

K. M. Uang, S. J. Wang, T.-M. Chen, W.-C. Lee, S.-L. Chen, Y.-Y. Wang, and H. Kuan, “Enhanced Performance of Vertical GaN-Based Light-Emitting Diodes with a Current-Blocking Layer and Electroplated Nickel Substrate,” Jpn. J. Appl. Phys. 48(10), 102101 (2009). [CrossRef]

10.

S.-J. Wang, S.-L. Chen, K.-M. Uang, W.-C. Lee, T.-M. Chen, C.-H. Chen, and B.-W. Liou, “The Use of Transparent Conducting Indium–Zinc Oxide Film as a Current Spreading Layer for Vertical-Structured High-Power GaN-Based Light-Emitting Diodes,” IEEE Photon. Technol. Lett. 18(10), 1146–1148 (2006). [CrossRef]

11.

J. P. Novak, M. D. Lay, F. K. Perkins, and E. S. Snow, “Macroelectronic applications of carbon nanotube networks,” Solid-State Electron. 48(10–11), 1753–1756 (2004). [CrossRef]

12.

L. Hu, D. S. Hecht, and G. Gruner, “Percolation in Transparent and Conducting Carbon Nanotube Networks,” Nano Lett. 4(12), 2513–2517 (2004). [CrossRef]

13.

R. C. Tenent, T. M. Barnes, J. D. Bergeson, A. J. Ferguson, B. To, L. M. Gedvilas, M. J. Heben, and J. L. Blackburn, “Ultrasmooth, Large‐Area, High‐Uniformity, Conductive Transparent Single‐Walled‐Carbon‐Nanotube Films for Photovoltaics Produced by Ultrasonic Spraying,” Adv. Mater. 21(31), 3210–3216 (2009). [CrossRef]

14.

M. A. Meitl, Y. Zhou, A. Gaur, S. Jeon, M. L. Usrey, M. S. Strano, and J. Rogers, “Solution Casting and Transfer Printing Single-Walled Carbon Nanotube Films,” Nano Lett. 4(9), 1643–1647 (2004). [CrossRef]

15.

M. W. Rowell, M. A. Topinka, M. D. McGehee, H. J. Prall, G. Dennler, N. S. Sariciftci, L. B. Hu, and G. Gruner, “Organic solar cells with carbon nanotube network electrodes,” Appl. Phys. Lett. 88(23), 233506 (2006). [CrossRef]

16.

T. V. Sreekumar, T. Liu, S. Kumar, L. M. Ericson, R. H. Hauge, and R. E. Smalley, “Single-Wall Carbon Nanotube Films,” Chem. Mater. 15(1), 175–178 (2003). [CrossRef]

17.

D. P. Long, J. L. Lazorcik, and R. Shashidhar, “Magnetically Directed Self-Assembly of Carbon Nanotube Devices,” Adv. Mater. 16(9–10), 815–819 (2004).

18.

S. Blatt, F. Hennrich, H. V. Löhneysen, M. M. Kappes, A. Vijayaraghavan, and R. Krupke, “Influence of Structural and Dielectric Anisotropy on the Dielectrophoresis of Single-Walled Carbon Nanotubes,” Nano Lett. 7(7), 1960–1966 (2007). [CrossRef] [PubMed]

19.

N. P. Armitage, J. C. P. Gabriel, and G. Gruner, “Quasi-Langmuir–Blodgett thin film deposition of carbon nanotubes,” J. Appl. Phys. 95(6), 3228 (2004). [CrossRef]

20.

K. H. Kim, C. W. Jang, T. G. Kim, S. Lee, S. H. Kim, and Y. T. Byun, “Processing Technique for Single-Walled Carbon Nanotube-Based Sensor Arrays,” J. Nanosci. Nanotechnol. 12(2), 1251–1255 (2012). [CrossRef] [PubMed]

21.

K. H. Kim, T. G. Kim, S. Lee, Y. M. Jhon, S. H. Kim, and Y. T. Byun, “Simple Assembling Technique of Single-Walled Carbon Nanotubed Using Only Photolithography,” J. Korean Phys. Soc. 58(5), 1380–1383 (2011).

22.

G. Xiao, Y. Tao, J. Lu, and Z. Zhang, “Highly conductive and transparent carbon nanotube composite thin films deposited on polyethylene terephthalate solution dipping,” Thin Solid Films 518(10), 2822–2824 (2010). [CrossRef]

23.

T. Wang, “Light Scattering Study on Single Wall Carbon Nanotube (SWNT) Dispersions,” MS. thesis, School of Polymer, Textile and Fiber Eng., Georgia Institute of Technology (2004).

24.

H. S. Woo, R. Czerw, S. Webster, D. L. Carroll, J. W. Park, and J. H. Lee, “Organic light emitting diodes fabricated with single wall carbon nanotubes dispersed in a hole conducting buffer: the role of carbon nanotubes in a hole conducting polymer,” Synth. Met. 116(1–3), 369–372 (2001). [CrossRef]

25.

J. Suh, H. Song, and E. K. Kim, “Enhancement of Photoluminescence from ZnO Film by Single Wall Carbon Nanotubes,” J. Nanosci. Nanotechnol. 11(7), 6148–6151 (2011). [CrossRef] [PubMed]

26.

D. S. Hecht, D. Thomas, L. B. Hu, C. Ladous, T. Lam, Y. Park, G. Irvin, and P. Drzaic, “Carbon-nanotube film on plastic as transparent electrode for resistive touch screens,” J. Soc. Inf. Disp. 17(11), 941–946 (2009). [CrossRef]

OCIS Codes
(230.3670) Optical devices : Light-emitting diodes
(250.0250) Optoelectronics : Optoelectronics
(160.4236) Materials : Nanomaterials

ToC Category:
Optical Devices

History
Original Manuscript: January 22, 2013
Revised Manuscript: March 15, 2013
Manuscript Accepted: March 18, 2013
Published: March 26, 2013

Citation
Su Jin Kim, Kyeong Heon Kim, and Tae Geun Kim, "Improved performance of GaN-based vertical light emitting diodes with conducting and transparent single-walled carbon nanotube networks," Opt. Express 21, 8062-8068 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-7-8062


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References

  1. C. F. Chu, C. C. Cheng, W. H. Liu, J. Y. Chu, F. H. Fan, H. C. Cheng, T. Doan, and C. A. Tran, “High brightness GaN vertical light-emitting diodes on metal alloy for general lighting application,” Proc. IEEE98(7), 1197–1207 (2010). [CrossRef]
  2. T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, “Increase in the extraction efficiency of GaN-based light-emitting diodes via surface roughening,” Appl. Phys. Lett.84(6), 855 (2004). [CrossRef]
  3. H. K. Cho, J. Jang, J. H. Choi, J. Choi, J. W. Kim, J. S. Lee, B. S. Lee, Y. H. Choe, K. D. Lee, S. H. Kim, K. Lee, S. K. Kim, and Y. H. Lee, “Light extraction enhancement from nano-imprinted photonic crystal GaN-based blue light-emitting diodes,” Opt. Express14(19), 8654–8660 (2006). [CrossRef] [PubMed]
  4. H.-M. An, J. I. Sim, K. S. Shin, Y. M. Sung, and T. G. Kim, “Increased light extraction from vertical GaN light-emitting diodes with ordered, cone-shaped deep-pillar nanostructures,” IEEE J. Quantum Electron.48(7), 891–896 (2012). [CrossRef]
  5. T. N. Oder, K. H. Kim, J. Y. Lin, and H. X. Jiang, “III-nitride blue and ultraviolet photonic crystal light emitting diodes,” Appl. Phys. Lett.84(4), 466–468 (2004). [CrossRef]
  6. Y. C. Shin, D. H. Kim, D. J. Chae, J. W. Yang, J. I. Shim, J. M. Park, K.-M. Ho, K. Constant, H. Y. Ryu, and T. G. Kim, “Effects of nanometer-scale photonic crystal structures on the light extraction from GaN light emitting diodes,” IEEE J. Quantum Electron.46(9), 1375–1380 (2010). [CrossRef]
  7. R. H. Horng, C. C. Yang, J. Y. Wu, S. H. Huang, C. E. Lee, and D. S. Wuu, “GaN-based light-emitting diodes with indium tin oxide texturing window layers using natural lithography,” Appl. Phys. Lett.86(22), 221101 (2005). [CrossRef]
  8. X. A. Cao, H. Piao, J. Li, J. Y. Lin, and H. X. Jiang, “Surface chemical and electronic properties of plasma-treated n-type Al0.5Ga0.5N,” Phys. Status Solidi204(10), 3410–3416 (2007) (a). [CrossRef]
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