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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 10 — May. 7, 2012
  • pp: 11423–11432
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Fabrication of SiNx-based photonic crystals on GaN-based LED devices with patterned sapphire substrate by nanoimprint lithography

Kyeong-Jae Byeon, Joong-Yeon Cho, Jinseung Kim, Hyoungwon Park, and Heon Lee  »View Author Affiliations


Optics Express, Vol. 20, Issue 10, pp. 11423-11432 (2012)
http://dx.doi.org/10.1364/OE.20.011423


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Abstract

SiNx-based photonic crystal (PhC) patterns were fabricated on the ITO electrode layer of a GaN-based light-emitting diode (LED) device on a patterned sapphire substrate (PSS) by a UV nanoimprint lithography process in order to improve the light extraction of the device. A three-dimensional finite-difference time-domain simulation confirmed that the light extraction of a GaN LED structure on a PSS is enhanced when SiNx PhC patterns are formed on the ITO top layer. From the I-V characteristics, the electrical properties of patterned LED devices with SiNx-based PhC were not degraded compared to the unpatterned LED device, since plasma etching of the p-GaN or the ITO layers was not involved in the patterning process. Additionally, the patterned LED devices with SiNx-based PhCs showed 19%-increased electroluminescence intensity compared with the unpatterned LED device at 445 nm wavelength when a 20 mA current is driven.

© 2012 OSA

1. Introduction

GaN-based light-emitting diodes (LEDs) have recently attracted significant attention for their diverse applications, such as backlighting in liquid crystal displays, traffic signal lamps, vehicle lamps and general illumination both indoors and outdoors. However, the external quantum efficiency of GaN-based LEDs is still not high enough to realize LED-based solid state lighting. The external quantum efficiency is mainly limited by low light extraction efficiency. One of the primary reasons for low light extraction efficiency is total internal reflection at the interface between a LED device and air, which is originated from the large difference in refractive index between GaN and air. By Snell’s law, the critical angle for a photon to escape from the device into air is about 24°, thus, a photon which propagates at an angle greater than the critical angle is guided and trapped inside the GaN-based LED device and is converted to heat, which degrades the performance and the durability of the device. Therefore, the enhancement of the light extraction is a crucial issue in improving the external quantum efficiency. To enhance the light extraction efficiency of GaN-based LEDs, various approaches, including the use of photonic crystals with large index contrast [1

1. J. J. Wierer Jr, A. David, and M. M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009). [CrossRef]

3

3. E. Matioli, S. Brinkley, K. M. Kelchner, S. Nakamura, S. DenBaars, J. Speck, and C. Weisbuch, “Polarized light extraction in m-plane GaN light-emitting diodes by embedded photonic-crystals,” Appl. Phys. Lett. 98(25), 251112 (2011). [CrossRef]

], microlens arrays [4

4. X.-H. Li, R. Song, Y.-K. Ee, P. Kumnorkaew, J. F. Gilchrist, and N. Tansu, “Light extraction efficiency and radiation patterns of III-nitride light-emitting diodes with colloidal microlens arrays with various aspect ratios,” IEEE Photonics J. 3(3), 489–499 (2011). [CrossRef]

6

6. M. Khizar, Z. Y. Fan, K. H. Kim, J. Y. Lin, and H. X. Jiang, “Nitride deep-ultraviolet light-emitting diodes with microlens array,” Appl. Phys. Lett. 86(17), 173504 (2005). [CrossRef]

], and self-assembled patterning [7

7. S. Chhajed, W. Lee, J. Cho, E. F. Schubert, and J. K. Kim, “Strong light extraction enhancement in GaInN light-emitting diodes by using self-organized nanoscale patterning of p-type GaN,” Appl. Phys. Lett. 98(7), 071102 (2011). [CrossRef]

] have been intensively conducted. The approach to address light extraction issue remains very important for achieving large external quantum efficiency in in GaN-based LEDs. In addition to the light extraction issue, it is important to note that achieving high internal quantum efficiency is also important for realizing InGaN-based LEDs with high external quantum efficiency. The charge separation issue has been an important limiting factor in achieving high internal quantum efficiency in InGaN quantum well (QW) LEDs [8

8. R. M. Farrell, E. C. Young, F. Wu, S. P. DenBaars, and J. S. Speck, “Materials and growth issues for high-performance nonpolar and semipolar light-emitting devices,” Semicond. Sci. Technol. 27(2), 024001 (2012). [CrossRef]

14

14. C.-H. Lu, C.-C. Lan, Y.-L. Lai, Y.-L. Li, and C.-P. Liu, “Enhancement of green emission from InGaN/GaN multiple quantum wells via coupling to surface plasmons in a two-dimensional silver array,” Adv. Funct. Mater. 21(24), 4719–4723 (2011). [CrossRef]

], especially for longer wavelength emission and high operating current density. Recent works for achieving high internal quantum efficiency in InGaN QW LEDs by charge separation suppression include semi/non-polar InGaN QW [8

8. R. M. Farrell, E. C. Young, F. Wu, S. P. DenBaars, and J. S. Speck, “Materials and growth issues for high-performance nonpolar and semipolar light-emitting devices,” Semicond. Sci. Technol. 27(2), 024001 (2012). [CrossRef]

,9

9. R. M. Farrell, D. A. Haeger, P. S. Hsu, K. Fujito, D. F. Feezell, S. P. DenBaars, J. S. Speck, and S. Nakamura, “Determination of internal parameters for AlGaN-cladding-free m-plane InGaN/GaN laser diodes,” Appl. Phys. Lett. 99(17), 171115 (2011). [CrossRef]

], c-plane InGaN QW with large overlap design [10

10. H. Zhao, G. Liu, J. Zhang, J. D. Poplawsky, V. Dierolf, and N. Tansu, “Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells,” Opt. Express 19(S4Suppl 4), A991–A1007 (2011). [CrossRef] [PubMed]

12

12. L. Zhang, K. Cheng, H. Liang, R. Lieten, M. Leys, and G. Borghs, “Photoluminescence studies of polarization effects in InGaN/(In)GaN multiple quantum well structures,” Jpn. J. Appl. Phys. 51, 030207 (2012). [CrossRef]

], surface plasmon coupled InGaN QWs [13

13. H. Zhao, J. Zhang, G. Liu, and N. Tansu, “Surface plasmon dispersion engineering via double-metallic Au/Ag layers for III-nitride based light-emitting diodes,” Appl. Phys. Lett. 98(15), 151115 (2011). [CrossRef]

,14

14. C.-H. Lu, C.-C. Lan, Y.-L. Lai, Y.-L. Li, and C.-P. Liu, “Enhancement of green emission from InGaN/GaN multiple quantum wells via coupling to surface plasmons in a two-dimensional silver array,” Adv. Funct. Mater. 21(24), 4719–4723 (2011). [CrossRef]

] approaches.

Especially, further enhancement of the external quantum efficiency of GaN-based LEDs on patterned sapphire substrates (PSSs) is greatly required. Most high quality GaN-based LEDs are fabricated on PSS in the current LED industry since the threading dislocation density in the epitaxial GaN layer is effectively reduced by the epitaxial lateral overgrowth and the micron-scaled patterns on the PSS act as scattering centers for the guided light inside LED devices [15

15. Y. J. Lee, J. M. Hwang, T. C. Hsu, M. H. Hsieh, M. J. Jou, B. J. Lee, T. C. Lu, H. C. Kuo, and S. C. Wang, “Enhancing the output power of GaN-based LEDs grown on wet-etched patterned sapphire substrates,” IEEE Photon. Technol. Lett. 18(10), 1152–1154 (2006). [CrossRef]

19

19. K. Tadatomo, H. Okagawa, Y. Ohuchi, T. Tsunekawa, T. Jyouichi, Y. Imada, M. Kato, H. Kudo, and T. Taguchi, “High output power InGaN ultraviolet light-emitting diodes fabricated on patterned substrates using metalorganic vapor phase epitaxy,” Phys. Status Solidi A 188(1), 121–125 (2001). [CrossRef]

]. The use of PSSs with micron-sized dimensions has led to increased in light extraction efficiency in GaN-based LEDs. Recently, Lin and associates had demonstrated that there exists a dependency on the pattern coverage density on extraction efficiency enhancement for GaN LEDs grown on the micron-sized PSSs [20

20. H. Y. Lin, Y. J. Chen, C. C. Chang, X. F. Li, S. C. Hsu, and C. Y. Liu, “Pattern-coverage effect on light extraction efficiency of GaN LED on patterned-sapphire substrate,” Electrochem. Solid-State Lett. 15(3), H72–H74 (2012). [CrossRef]

]. However, it is important to note that recent works by using nanoscale PSSs had also led to increase in internal quantum efficiency and light extraction efficiency in InGaN-based LEDs [21

21. Y. Li, S. You, M. Zhu, L. Zhao, W. Hou, T. Detchprohm, Y. Taniguchi, N. Tamura, S. Tanaka, and C. Wetzel, “Defect-reduced green GaInN/GaN light-emitting diode on nanopatterned sapphire,” Appl. Phys. Lett. 98(15), 151102 (2011). [CrossRef]

24

24. T. Shinagawa, Y. Abe, H. Matsumoto, B. Li, K. Murakami, N. Okada, K. Tadatomo, M. Kannaka, and H. Fujii, “Light-emitting diodes fabricated on nanopatterned sapphire substrates by thermal lithography,” Phys. Status Solidi C 7(7-8), 2165–2167 (2010). [CrossRef]

], as a result of two order-of-magnitude reduction in threading dislocation [21

21. Y. Li, S. You, M. Zhu, L. Zhao, W. Hou, T. Detchprohm, Y. Taniguchi, N. Tamura, S. Tanaka, and C. Wetzel, “Defect-reduced green GaInN/GaN light-emitting diode on nanopatterned sapphire,” Appl. Phys. Lett. 98(15), 151102 (2011). [CrossRef]

], reduction in screw dislocation density [22

22. W. Cao, J. M. Biser, Y.-K. Ee, X.-H. Li, N. Tansu, H. M. Chan, and R. P. Vinci, “Dislocation structure of GaN films grown on planar and nanopatterned sapphire,” J. Appl. Phys. 110(5), 053505 (2011). [CrossRef]

], and increase in light scattering by nano-scaled pattern [23

23. C.-C. Kao, Y.-K. Su, C.-L. Lin, and J.-J. Chen, “The aspect ratio effects on the performances of GaN-based light-emitting diodes with nanopatterned sapphire substrates,” Appl. Phys. Lett. 97(2), 023111 (2010). [CrossRef]

,24

24. T. Shinagawa, Y. Abe, H. Matsumoto, B. Li, K. Murakami, N. Okada, K. Tadatomo, M. Kannaka, and H. Fujii, “Light-emitting diodes fabricated on nanopatterned sapphire substrates by thermal lithography,” Phys. Status Solidi C 7(7-8), 2165–2167 (2010). [CrossRef]

]. Although both the internal quantum efficiency and light extraction efficiency of GaN-based LEDs are enhanced by the PSS, a further increase of the light extraction is essential for the realization of high brightness and high efficiency LEDs.

In this study, SiNx-based photonic crystal (PhC) structures are formed on the GaN-based LEDs, fabricated on the PSS, in order to increase the external quantum efficiency by nanoimprint lithography (NIL) [25

25. K.-J. Byeon, S.-Y. Hwang, and H. Lee, “Fabrication of two-dimensional photonic crystal patterns on GaN-based light-emitting diodes using thermally curable monomer-based nanoimprint lithography,” Appl. Phys. Lett. 91(9), 091106 (2007). [CrossRef]

29

29. T. A. Truong, L. M. Campos, E. Matioli, I. Meinel, C. J. Hawker, C. Weisbuch, and P. M. Petroff, “Light extraction from GaN-based light emitting diode structures with a noninvasive two-dimensional photonic crystal,” Appl. Phys. Lett. 94(2), 023101 (2009). [CrossRef]

], which offers low cost and high throughput compared to other lithography techniques such as photolithography [30

30. M.-H. Wu and G. M. Whitesides, “Fabrication of arrays of two-dimensional micropatterns using microspheres as lenses for projection photolithography,” Appl. Phys. Lett. 78(16), 2273–2275 (2001). [CrossRef]

], e-beam lithography [31

31. M. De Vittorio, M. T. Todaro, T. Stomeo, R. Cingolani, D. Cojoc, and E. D. Fabrizio, “Two-dimensional photonic crystal waveguide obtained by e-beam direct writing of SU8-2000 photoresist,” Microelectron. Eng. 73–74, 388–391 (2004). [CrossRef]

] and so on. Prior to the NIL process, we analyzed the effect of the presence of the SiNx-based PhC on the light extraction of a GaN LED structure on a PSS using a three-dimensional finite-difference time-domain (FDTD) simulation tool. In addition, the optical and electrical properties of the patterned LED devices with SiNx-based PhC were confirmed by the electroluminescence (EL) and the I-V characteristics.

2. Experimental details

A typical GaN-based blue LED structure was grown on a (0001)-oriented PSS by a conventional MOCVD process. After the deposition of a thin low-temperature GaN buffer layer, the LED structure, which consists of layers of 5 µm thick un-doped GaN, 3 µm thick n-GaN, 50 nm thick InGaN/GaN multi QWs and 150 nm thick p-GaN, was fabricated. Then, a 200 nm thick ITO layer was sputtered onto the p-GaN layer to achieve current spreading between the p-pad metal and the p-GaN layer.

Figure 1
Fig. 1 The fabrication process of the patterned LED device with SiNx-based PhCs on the ITO electrode of the GaN-based LED by using NIL and reactive ion etching processes.
shows the overall patterning process for the fabrication of the SiNx-based PhC pattern on the LED structure. First, SiO2/SiNx was deposited on the ITO layer by a PECVD process. The thickness of the SiO2 layer was about 70 nm and the thickness of the SiNx layers was split between 300 nm and 500 nm in order to fabricate PhC patterns with different heights. After the PECVD process, a 200 nm thick LOL 2000TM sacrificial polymer layer was coated on the SiNx layer, followed by a UV NIL process at 20 atm of pressure while exposing the stack of the mold/resin/LED wafer to UV for 10 min. In the UV NIL process, a flexible polymer-based mold was used for conformal contact with the LED wafer [32

32. K.-J. Byeon, E.-J. Hong, H. Park, J.-Y. Cho, S.-H. Lee, J. Jhin, J. H. Baek, and H. Lee, “Full wafer scale nanoimprint lithography for GaN-based light-emitting diodes,” Thin Solid Films 519(7), 2241–2246 (2011). [CrossRef]

]. A UV-curable resin composed of 65 wt% of benzylmethacrylate base monomer, 5 wt % of IrgacureTM 184 UV initiator and 30 wt% of methacryloxypropyl-terminated polydimethylsiloxanes, was used for the UV NIL to elevate the etch resistance to the oxygen plasma [33

33. S. Y. Hwang, H. Y. Jung, J.-H. Jeong, and H. Lee, “Fabrication of nano-sized metal patterns on flexible polyethylene-terephthalate substrate using bi-layer nanoimprint lithography,” Thin Solid Films 517(14), 4104–4107 (2009). [CrossRef]

]. After the UV NIL process, the sacrificial polymer layer under the imprinted pattern was cleared off with an oxygen plasma treatment. Next, a 50 nm thick Cr layer was deposited by e-beam evaporation and was lifted off the SiNx layer by removing the pattern, which was composed of the imprint resin/polymer sacrificial layer, with dimethylformamide solution. Finally, the masked SiNx layer with the Cr pattern was etched by a reactive ion etching process using CF4 plasma and then the SiNx-based PhC patterns were formed on the LED structure.

To fabricate LED devices, at first, a photo-resist was coated onto the patterned LED wafer and was partially removed by photolithography to establish the contact region for p- and n-GaN. Prior to mesa etching, SiNx-based PhC patterns on the contact region for p- and n-GaN, which is not covered with the photo-resist, were removed along with the underlying SiO2 layer by dipping the sample in buffered oxide etcher solution. Through mesa etching using ICP and deposition of p- and n-pad metals, composed of Cr/Au, 300 µm x 300 µm conventional lateral-type LED devices were fabricated. To analyze the optical and electrical properties of the patterned LED devices, measurements of EL and I-V characteristics were conducted. A three-dimensional FDTD simulation on light extraction of the patterned LED structures was carried out using a commercially available FullWAVETM simulator [34

34. FullWAVE 6.1, Rsoft Design Group, Inc., http://www.rsoftdesign.com

36

36. K.-J. Byeon, H. Park, J.-Y. Cho, K.-Y. Yang, J. H. Baek, G. Y. Jung, and H. Lee, “Fabrication of photonic crystal structure on indium tin oxide electrode of GaN-based light-emitting diodes,” Phys. Status Solidi A 208(2), 480–483 (2011). [CrossRef]

].

3. Results and discussion

In Fig. 2
Fig. 2 (a)–(c) are cross sectional, tilted and top views of SEM micrographs of 300 nm-high SiNx PhC patterns on the ITO electrode, respectively. (d)–(f) are also cross sectional, tilted and top views of SEM micrographs of 500 nm-high SiNx PhC patterns on the ITO electrode, respectively.
, SiNx-based PhC patterns with heights of 300 nm and 500 nm, fabricated by the NIL and RIE processes, are shown. Figures 2(a) to 2(c) and Figs. 2(d) to 2(f) are SEM images of the cross-sectional, tilted and top views of PhC patterns with heights of 300 nm and 500 nm, respectively. Each well-aligned PhC pattern on the ITO electrode layer has a diameter of 250 nm and a pitch of 600 nm. Due to the difference of the etch resistance to CF4 plasma between the SiO2 and the SiNx layers, PhC patterns slightly display re-entrance etch-profiles. In this work, the etch rates of SiO2 and SiNx layers, deposited by PECVD, were about 25 nm/min and 50 nm/min, respectively. This re-entrance profile is clearer in the PhC pattern of 500 nm in height than the PhC pattern of 300 nm in height. Figure 3(a)
Fig. 3 (a) Top and (b) cross sectional SEM images of the LED device with the SiNx PhC pattern.
is the top SEM image of the fabricated LED device with the SiNx PhC pattern. The SiNx PhC pattern was only formed on the ITO top electrode layer of the LED device. Thus, there is no problem in forming the p- and n-pad metals on the p-GaN and n-GaN, respectively. Figure 3(b) is the cross-sectional SEM image of the GaN-based LED structure with the SiNx PhC pattern, which was grown on the PSS with a diameter of 2.5 µm and a height of 1.5 µm. As shown in Fig. 3(b), the array of SiNx PhC patterns was uniformly fabricated on the ITO electrode layer of the GaN-based LED.

To investigate the effect of the presence of the SiNx-based PhC patterns with different heights on the light extraction of LED structures, a three-dimensional FDTD simulation was conducted. Figures 4(a)
Fig. 4 Simplified FDTD simulation designs of (a) the conventional LED, (b) the LED with the PSS and (c) the LED with SiNx-PhC patterns and the PSS.
to 4(c) are schematic diagrams of the simplified LED structures for the FDTD simulation, which are composed of a 200 nm thick ITO, a 9 µm thick GaN and 2 µm thick sapphire layers. The plane of continuous polarized dipoles was placed at 150 nm below the GaN surface as the light source which emits photons in random directions and the wavelength of the light source was set to 450 nm. The area of the simulation domain is limited to 3 µm x 5.1 µm and only the 300 nm-thick sapphire layer was partially involved in the simulation domain, in order to avoid the FDTD calculation being hugely time consuming. Three different LED structures, consisting of an LED on a flat sapphire substrate, an LED on PSS and an SiNx-PhC patterned LED on PSS, were considered as shown in Figs. 4(a) to 4(c). The lens-shaped PSS pattern in the simulation structure has a 2 µm diameter, 3 µm pitch and 1 µm height and is pseudo-hexagonally arrayed. The SiNx-PhC pattern in the simulation structure has a 300 nm diameter and 600 nm pitch and its height is split into levels from 100 nm to 900 nm with an increment of 200 nm. The grid size of the FDTD was set to 10 nm for reliable simulation computation, and periodic boundary conditions were applied to the x-y plane in order to minimize the effect of the small size of the simulation domain.

Figure 5
Fig. 5 FDTD simulation results on light extraction of the conventional LED, the LED on the PSS and the SiNx-PhC patterned LED.
presents the results of the FDTD simulation for the considered LED structures, which are described in Fig. 4. By inserting the PSS into the normal LED structure, the light extraction efficiency was increased by 18.75%. This agrees well with lots of reports that a PSS is helpful in enhancing the light extraction of LEDs, as well as improving the crystal quality of GaN by reducing the threading dislocation density. When the SiNx-based PhC pattern with 300 nm of height is formed on the ITO top layer of the GaN LED structure, the light extraction efficiency was increased by up to 14.80%. Thus, from the simulation result, we confirmed further enhancement in the light extraction of a GaN-based LED on a PSS by introducing the additional patterned layer. This simulation method did not take into account the photon recycling and reabsorption process, thus this method may not provide the accurate absolute value of the light extraction efficiency. However, the use of this method is sufficient for providing comparison of the light extraction efficiency among all the LEDs.

We measured the I-V characteristics of the unpatterned and SiNx-based PhC patterned LED devices, which were all fabricated on the PSS, as shown in Fig. 6
Fig. 6 The I-V characteristics of the un-patterned LED device and LED devices with SiNx-PhC patterns of 300 nm and 500 nm in height. All LED devices were fabricated on the PSS. The inset shows the I-V characteristics on a logarithmic scale.
. The forward voltages of all LED devices are in the 4.1 V to 4.2 V range at 20 mA drive current. The inset in Fig. 6 shows that the I-V characteristics of the patterned LEDs exhibited reduction in leakage current, in comparison to that of the unpatterned LED. This result can be explained by the presence of the thin SiO2 layer on the ITO electrode, which acts as a surface passivation layer to prevent surface leakage [37

37. S. J. Chang, C. S. Chang, Y. K. Su, R. W. Chuang, Y. C. Lin, S. C. Shei, H. M. Lo, H. Y. Lin, and J. C. Ke, “Highly reliable nitride-based LEDs with SPS+ITO upper contacts,” IEEE J. Quantum Electron. 39(11), 1439–1443 (2003). [CrossRef]

, 38

38. Y. Z. Chiou, “Leakage current analysis of nitride-based photodetectors by emission microscopy inspection,” IEEE Sens. J. 8(9), 1506–1510 (2008). [CrossRef]

]. Thus, the electrical properties of the patterned LED devices with SiNx-based PhC were not degraded since no plasma etching process was conducted in the p-GaN layer while fabricating the SiNx-based PhC pattern on the ITO electrode.

In order to confirm the effect of the presence of SiNx PhC pattern on the light extraction of the LED device, which was fabricated on the PSS, we measured the EL intensities of the unpatterned LED device and the patterned LED devices with SiNx PhC patterns, as shown in Fig. 7
Fig. 7 (a) EL intensity at 20 mA current and (b) EL intensity versus injection current at a wavelength of 445 nm for the un-patterned LED device and the patterned LED devices with SiNx-based PhCs.
. When 20 mA of current is injected, the EL intensities of the LED devices with SiNx-based PhC patterns of 300 nm and 500 nm in height were increased by 14.5% and 19%, respectively, compared to that of the unpatterned LED device at a wavelength of 445 nm, as shown in Fig. 7(a). In contrast to the simulation results, the LED device with the 300 nm-high SiNx-based PhC pattern showed stronger EL intensity than the LED device with the 500 nm-high SiNx-based PhC pattern. The different tendencies shown by the EL and the simulation might result from slight differences in structure between the fabricated SiNx-based PhC pattern and the designed SiNx-PhC pattern in the simulation, including the diameter and profile. So far, most studies on the light extraction of LEDs have been performed on LEDs with flat sapphire substrates. Enhancing the light extraction of LEDs on PSS is relatively more difficult than it is for LEDs on flat sapphire substrates since the light extraction efficiency is already enhanced by the PSS. However, further increase in the light extraction of the LED device on the PSS was confirmed by forming the SiNx-based PhC patterns, which suppress the total internal reflection. The EL intensity according to injection current at a wavelength of 445 nm is shown in Fig. 7(b). At every injection current, the patterned LED devices with SiNx-based PhCs showed higher EL intensity than the unpatterned LED device.

4. Conclusion

SiNx-based PhC patterns were formed on GaN-based LED devices fabricated on PSS by the UV-NIL process in order to enhance the light extraction efficiency. From the three-dimensional FDTD simulation, when the height of the SiNx-pattern is 300 nm, the light extraction efficiency of the SiNx-PhC patterned LED structure on the PSS was increased by up to 14.80% compared to the unpatterned LED structure on the PSS. Similar to the simulation results, the SiNx-based PhC patterned LED device on the PSS showed an increase in EL intensity of up to 19% compared to an unpatterned LED device on the PSS at 20 mA drive current. Thus, total internal reflection was suppressed inside the GaN-based LED device by inserting SiNx-based PhC patterns. Moreover, the electrical properties of all patterned LED devices were not degraded because plasma etching of the p-GaN layer was not performed in the patterning process.

Acknowledgments

This research was supported by the R&D program for Industrial Core Technology through the Korea Evaluation Institute of Industrial Technology supported by the Ministry of Knowledge Economy in Korea (Grant No. 10040225). This research was also supported by Technology Innovation Program funded by the Ministry of Knowledge Economy (20103020010020-11-2-100).

References and links

1.

J. J. Wierer Jr, A. David, and M. M. Megens, “III-nitride photonic-crystal light-emitting diodes with high extraction efficiency,” Nat. Photonics 3(3), 163–169 (2009). [CrossRef]

2.

E. Rangel, E. Matioli, Y.-S. Choi, C. Weisbuch, J. S. Speck, and E. L. Hu, “Directionality control through selective excitation of low-order guided modes in thin-film InGaN photonic crystal light-emitting diodes,” Appl. Phys. Lett. 98(8), 081104 (2011). [CrossRef]

3.

E. Matioli, S. Brinkley, K. M. Kelchner, S. Nakamura, S. DenBaars, J. Speck, and C. Weisbuch, “Polarized light extraction in m-plane GaN light-emitting diodes by embedded photonic-crystals,” Appl. Phys. Lett. 98(25), 251112 (2011). [CrossRef]

4.

X.-H. Li, R. Song, Y.-K. Ee, P. Kumnorkaew, J. F. Gilchrist, and N. Tansu, “Light extraction efficiency and radiation patterns of III-nitride light-emitting diodes with colloidal microlens arrays with various aspect ratios,” IEEE Photonics J. 3(3), 489–499 (2011). [CrossRef]

5.

D. Kim, H. Lee, N. Cho, Y. Sung, and G. Yeom, “Effect of GaN microlens array on efficiency of GaN-based blue-light-emitting diodes,” Jpn. J. Appl. Phys. 44(1), L18–L20 (2005). [CrossRef]

6.

M. Khizar, Z. Y. Fan, K. H. Kim, J. Y. Lin, and H. X. Jiang, “Nitride deep-ultraviolet light-emitting diodes with microlens array,” Appl. Phys. Lett. 86(17), 173504 (2005). [CrossRef]

7.

S. Chhajed, W. Lee, J. Cho, E. F. Schubert, and J. K. Kim, “Strong light extraction enhancement in GaInN light-emitting diodes by using self-organized nanoscale patterning of p-type GaN,” Appl. Phys. Lett. 98(7), 071102 (2011). [CrossRef]

8.

R. M. Farrell, E. C. Young, F. Wu, S. P. DenBaars, and J. S. Speck, “Materials and growth issues for high-performance nonpolar and semipolar light-emitting devices,” Semicond. Sci. Technol. 27(2), 024001 (2012). [CrossRef]

9.

R. M. Farrell, D. A. Haeger, P. S. Hsu, K. Fujito, D. F. Feezell, S. P. DenBaars, J. S. Speck, and S. Nakamura, “Determination of internal parameters for AlGaN-cladding-free m-plane InGaN/GaN laser diodes,” Appl. Phys. Lett. 99(17), 171115 (2011). [CrossRef]

10.

H. Zhao, G. Liu, J. Zhang, J. D. Poplawsky, V. Dierolf, and N. Tansu, “Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells,” Opt. Express 19(S4Suppl 4), A991–A1007 (2011). [CrossRef] [PubMed]

11.

J. Zhang and N. Tansu, “Improvement in spontaneous emission rates for InGaN quantum wells on ternary InGaN substrate for light-emitting diodes,” J. Appl. Phys. 110(11), 113110 (2011). [CrossRef]

12.

L. Zhang, K. Cheng, H. Liang, R. Lieten, M. Leys, and G. Borghs, “Photoluminescence studies of polarization effects in InGaN/(In)GaN multiple quantum well structures,” Jpn. J. Appl. Phys. 51, 030207 (2012). [CrossRef]

13.

H. Zhao, J. Zhang, G. Liu, and N. Tansu, “Surface plasmon dispersion engineering via double-metallic Au/Ag layers for III-nitride based light-emitting diodes,” Appl. Phys. Lett. 98(15), 151115 (2011). [CrossRef]

14.

C.-H. Lu, C.-C. Lan, Y.-L. Lai, Y.-L. Li, and C.-P. Liu, “Enhancement of green emission from InGaN/GaN multiple quantum wells via coupling to surface plasmons in a two-dimensional silver array,” Adv. Funct. Mater. 21(24), 4719–4723 (2011). [CrossRef]

15.

Y. J. Lee, J. M. Hwang, T. C. Hsu, M. H. Hsieh, M. J. Jou, B. J. Lee, T. C. Lu, H. C. Kuo, and S. C. Wang, “Enhancing the output power of GaN-based LEDs grown on wet-etched patterned sapphire substrates,” IEEE Photon. Technol. Lett. 18(10), 1152–1154 (2006). [CrossRef]

16.

D. S. Wuu, W. K. Wang, K. S. Wen, S. C. Huang, S. H. Lin, S. Y. Huang, C. F. Lin, and R. H. Horng, “Defect reduction and efficiency improvement of near-ultraviolet emitters via laterally overgrown GaN on a GaN/patterned sapphire template,” Appl. Phys. Lett. 89(16), 161105 (2006). [CrossRef]

17.

Z. H. Feng, Y. D. Qi, Z. D. Lu, and K. M. Lau, “GaN-based blue light-emitting diodes grown and fabricated on patterned sapphire substrates by metalorganic vapor-phase epitaxy,” J. Cryst. Growth 272(1-4), 327–332 (2004). [CrossRef]

18.

X.-H. Huang, J.-P. Liu, J.-J. Kong, H. Yang, and H.-B. Wang, “High-efficiency InGaN-based LEDs grown on patterned sapphire substrates,” Opt. Express 19(S4Suppl 4), A949–A955 (2011). [CrossRef] [PubMed]

19.

K. Tadatomo, H. Okagawa, Y. Ohuchi, T. Tsunekawa, T. Jyouichi, Y. Imada, M. Kato, H. Kudo, and T. Taguchi, “High output power InGaN ultraviolet light-emitting diodes fabricated on patterned substrates using metalorganic vapor phase epitaxy,” Phys. Status Solidi A 188(1), 121–125 (2001). [CrossRef]

20.

H. Y. Lin, Y. J. Chen, C. C. Chang, X. F. Li, S. C. Hsu, and C. Y. Liu, “Pattern-coverage effect on light extraction efficiency of GaN LED on patterned-sapphire substrate,” Electrochem. Solid-State Lett. 15(3), H72–H74 (2012). [CrossRef]

21.

Y. Li, S. You, M. Zhu, L. Zhao, W. Hou, T. Detchprohm, Y. Taniguchi, N. Tamura, S. Tanaka, and C. Wetzel, “Defect-reduced green GaInN/GaN light-emitting diode on nanopatterned sapphire,” Appl. Phys. Lett. 98(15), 151102 (2011). [CrossRef]

22.

W. Cao, J. M. Biser, Y.-K. Ee, X.-H. Li, N. Tansu, H. M. Chan, and R. P. Vinci, “Dislocation structure of GaN films grown on planar and nanopatterned sapphire,” J. Appl. Phys. 110(5), 053505 (2011). [CrossRef]

23.

C.-C. Kao, Y.-K. Su, C.-L. Lin, and J.-J. Chen, “The aspect ratio effects on the performances of GaN-based light-emitting diodes with nanopatterned sapphire substrates,” Appl. Phys. Lett. 97(2), 023111 (2010). [CrossRef]

24.

T. Shinagawa, Y. Abe, H. Matsumoto, B. Li, K. Murakami, N. Okada, K. Tadatomo, M. Kannaka, and H. Fujii, “Light-emitting diodes fabricated on nanopatterned sapphire substrates by thermal lithography,” Phys. Status Solidi C 7(7-8), 2165–2167 (2010). [CrossRef]

25.

K.-J. Byeon, S.-Y. Hwang, and H. Lee, “Fabrication of two-dimensional photonic crystal patterns on GaN-based light-emitting diodes using thermally curable monomer-based nanoimprint lithography,” Appl. Phys. Lett. 91(9), 091106 (2007). [CrossRef]

26.

L. J. Guo, “Recent progress in nanoimprint technology and its applications,” J. Phys. D Appl. Phys. 37(11), R123–R141 (2004). [CrossRef]

27.

F. S. Diana, A. David, I. Meinel, R. Sharma, C. Weisbuch, S. Nakamura, and P. M. Petroff, “Photonic crystal-assisted light extraction from a colloidal quantum dot/GaN hybrid structure,” Nano Lett. 6(6), 1116–1120 (2006). [CrossRef] [PubMed]

28.

H. K. Cho, J. Jang, J.-H. Choi, J. Choi, J. Kim, J. S. Lee, B. 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]

29.

T. A. Truong, L. M. Campos, E. Matioli, I. Meinel, C. J. Hawker, C. Weisbuch, and P. M. Petroff, “Light extraction from GaN-based light emitting diode structures with a noninvasive two-dimensional photonic crystal,” Appl. Phys. Lett. 94(2), 023101 (2009). [CrossRef]

30.

M.-H. Wu and G. M. Whitesides, “Fabrication of arrays of two-dimensional micropatterns using microspheres as lenses for projection photolithography,” Appl. Phys. Lett. 78(16), 2273–2275 (2001). [CrossRef]

31.

M. De Vittorio, M. T. Todaro, T. Stomeo, R. Cingolani, D. Cojoc, and E. D. Fabrizio, “Two-dimensional photonic crystal waveguide obtained by e-beam direct writing of SU8-2000 photoresist,” Microelectron. Eng. 73–74, 388–391 (2004). [CrossRef]

32.

K.-J. Byeon, E.-J. Hong, H. Park, J.-Y. Cho, S.-H. Lee, J. Jhin, J. H. Baek, and H. Lee, “Full wafer scale nanoimprint lithography for GaN-based light-emitting diodes,” Thin Solid Films 519(7), 2241–2246 (2011). [CrossRef]

33.

S. Y. Hwang, H. Y. Jung, J.-H. Jeong, and H. Lee, “Fabrication of nano-sized metal patterns on flexible polyethylene-terephthalate substrate using bi-layer nanoimprint lithography,” Thin Solid Films 517(14), 4104–4107 (2009). [CrossRef]

34.

FullWAVE 6.1, Rsoft Design Group, Inc., http://www.rsoftdesign.com

35.

C.-C. Wang, H. Ku, C.-C. Liu, K.-K. Chong, C.-I. Hung, Y.-H. Wang, and M.-P. Houng, “Enhancement of the light output performance for GaN-based light-emitting diodes by bottom pillar structure,” Appl. Phys. Lett. 91(12), 121109 (2007). [CrossRef]

36.

K.-J. Byeon, H. Park, J.-Y. Cho, K.-Y. Yang, J. H. Baek, G. Y. Jung, and H. Lee, “Fabrication of photonic crystal structure on indium tin oxide electrode of GaN-based light-emitting diodes,” Phys. Status Solidi A 208(2), 480–483 (2011). [CrossRef]

37.

S. J. Chang, C. S. Chang, Y. K. Su, R. W. Chuang, Y. C. Lin, S. C. Shei, H. M. Lo, H. Y. Lin, and J. C. Ke, “Highly reliable nitride-based LEDs with SPS+ITO upper contacts,” IEEE J. Quantum Electron. 39(11), 1439–1443 (2003). [CrossRef]

38.

Y. Z. Chiou, “Leakage current analysis of nitride-based photodetectors by emission microscopy inspection,” IEEE Sens. J. 8(9), 1506–1510 (2008). [CrossRef]

OCIS Codes
(230.0230) Optical devices : Optical devices
(230.3670) Optical devices : Light-emitting diodes
(250.0250) Optoelectronics : Optoelectronics
(220.4241) Optical design and fabrication : Nanostructure fabrication
(230.5298) Optical devices : Photonic crystals

ToC Category:
Optical Devices

History
Original Manuscript: March 9, 2012
Revised Manuscript: April 26, 2012
Manuscript Accepted: April 27, 2012
Published: May 4, 2012

Citation
Kyeong-Jae Byeon, Joong-Yeon Cho, Jinseung Kim, Hyoungwon Park, and Heon Lee, "Fabrication of SiNx-based photonic crystals on GaN-based LED devices with patterned sapphire substrate by nanoimprint lithography," Opt. Express 20, 11423-11432 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-10-11423


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References

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  15. Y. J. Lee, J. M. Hwang, T. C. Hsu, M. H. Hsieh, M. J. Jou, B. J. Lee, T. C. Lu, H. C. Kuo, and S. C. Wang, “Enhancing the output power of GaN-based LEDs grown on wet-etched patterned sapphire substrates,” IEEE Photon. Technol. Lett.18(10), 1152–1154 (2006). [CrossRef]
  16. D. S. Wuu, W. K. Wang, K. S. Wen, S. C. Huang, S. H. Lin, S. Y. Huang, C. F. Lin, and R. H. Horng, “Defect reduction and efficiency improvement of near-ultraviolet emitters via laterally overgrown GaN on a GaN/patterned sapphire template,” Appl. Phys. Lett.89(16), 161105 (2006). [CrossRef]
  17. Z. H. Feng, Y. D. Qi, Z. D. Lu, and K. M. Lau, “GaN-based blue light-emitting diodes grown and fabricated on patterned sapphire substrates by metalorganic vapor-phase epitaxy,” J. Cryst. Growth272(1-4), 327–332 (2004). [CrossRef]
  18. X.-H. Huang, J.-P. Liu, J.-J. Kong, H. Yang, and H.-B. Wang, “High-efficiency InGaN-based LEDs grown on patterned sapphire substrates,” Opt. Express19(S4Suppl 4), A949–A955 (2011). [CrossRef] [PubMed]
  19. K. Tadatomo, H. Okagawa, Y. Ohuchi, T. Tsunekawa, T. Jyouichi, Y. Imada, M. Kato, H. Kudo, and T. Taguchi, “High output power InGaN ultraviolet light-emitting diodes fabricated on patterned substrates using metalorganic vapor phase epitaxy,” Phys. Status Solidi A188(1), 121–125 (2001). [CrossRef]
  20. H. Y. Lin, Y. J. Chen, C. C. Chang, X. F. Li, S. C. Hsu, and C. Y. Liu, “Pattern-coverage effect on light extraction efficiency of GaN LED on patterned-sapphire substrate,” Electrochem. Solid-State Lett.15(3), H72–H74 (2012). [CrossRef]
  21. Y. Li, S. You, M. Zhu, L. Zhao, W. Hou, T. Detchprohm, Y. Taniguchi, N. Tamura, S. Tanaka, and C. Wetzel, “Defect-reduced green GaInN/GaN light-emitting diode on nanopatterned sapphire,” Appl. Phys. Lett.98(15), 151102 (2011). [CrossRef]
  22. W. Cao, J. M. Biser, Y.-K. Ee, X.-H. Li, N. Tansu, H. M. Chan, and R. P. Vinci, “Dislocation structure of GaN films grown on planar and nanopatterned sapphire,” J. Appl. Phys.110(5), 053505 (2011). [CrossRef]
  23. C.-C. Kao, Y.-K. Su, C.-L. Lin, and J.-J. Chen, “The aspect ratio effects on the performances of GaN-based light-emitting diodes with nanopatterned sapphire substrates,” Appl. Phys. Lett.97(2), 023111 (2010). [CrossRef]
  24. T. Shinagawa, Y. Abe, H. Matsumoto, B. Li, K. Murakami, N. Okada, K. Tadatomo, M. Kannaka, and H. Fujii, “Light-emitting diodes fabricated on nanopatterned sapphire substrates by thermal lithography,” Phys. Status Solidi C7(7-8), 2165–2167 (2010). [CrossRef]
  25. K.-J. Byeon, S.-Y. Hwang, and H. Lee, “Fabrication of two-dimensional photonic crystal patterns on GaN-based light-emitting diodes using thermally curable monomer-based nanoimprint lithography,” Appl. Phys. Lett.91(9), 091106 (2007). [CrossRef]
  26. L. J. Guo, “Recent progress in nanoimprint technology and its applications,” J. Phys. D Appl. Phys.37(11), R123–R141 (2004). [CrossRef]
  27. F. S. Diana, A. David, I. Meinel, R. Sharma, C. Weisbuch, S. Nakamura, and P. M. Petroff, “Photonic crystal-assisted light extraction from a colloidal quantum dot/GaN hybrid structure,” Nano Lett.6(6), 1116–1120 (2006). [CrossRef] [PubMed]
  28. H. K. Cho, J. Jang, J.-H. Choi, J. Choi, J. Kim, J. S. Lee, B. 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]
  29. T. A. Truong, L. M. Campos, E. Matioli, I. Meinel, C. J. Hawker, C. Weisbuch, and P. M. Petroff, “Light extraction from GaN-based light emitting diode structures with a noninvasive two-dimensional photonic crystal,” Appl. Phys. Lett.94(2), 023101 (2009). [CrossRef]
  30. M.-H. Wu and G. M. Whitesides, “Fabrication of arrays of two-dimensional micropatterns using microspheres as lenses for projection photolithography,” Appl. Phys. Lett.78(16), 2273–2275 (2001). [CrossRef]
  31. M. De Vittorio, M. T. Todaro, T. Stomeo, R. Cingolani, D. Cojoc, and E. D. Fabrizio, “Two-dimensional photonic crystal waveguide obtained by e-beam direct writing of SU8-2000 photoresist,” Microelectron. Eng.73–74, 388–391 (2004). [CrossRef]
  32. K.-J. Byeon, E.-J. Hong, H. Park, J.-Y. Cho, S.-H. Lee, J. Jhin, J. H. Baek, and H. Lee, “Full wafer scale nanoimprint lithography for GaN-based light-emitting diodes,” Thin Solid Films519(7), 2241–2246 (2011). [CrossRef]
  33. S. Y. Hwang, H. Y. Jung, J.-H. Jeong, and H. Lee, “Fabrication of nano-sized metal patterns on flexible polyethylene-terephthalate substrate using bi-layer nanoimprint lithography,” Thin Solid Films517(14), 4104–4107 (2009). [CrossRef]
  34. FullWAVE 6.1, Rsoft Design Group, Inc., http://www.rsoftdesign.com
  35. C.-C. Wang, H. Ku, C.-C. Liu, K.-K. Chong, C.-I. Hung, Y.-H. Wang, and M.-P. Houng, “Enhancement of the light output performance for GaN-based light-emitting diodes by bottom pillar structure,” Appl. Phys. Lett.91(12), 121109 (2007). [CrossRef]
  36. K.-J. Byeon, H. Park, J.-Y. Cho, K.-Y. Yang, J. H. Baek, G. Y. Jung, and H. Lee, “Fabrication of photonic crystal structure on indium tin oxide electrode of GaN-based light-emitting diodes,” Phys. Status Solidi A208(2), 480–483 (2011). [CrossRef]
  37. S. J. Chang, C. S. Chang, Y. K. Su, R. W. Chuang, Y. C. Lin, S. C. Shei, H. M. Lo, H. Y. Lin, and J. C. Ke, “Highly reliable nitride-based LEDs with SPS+ITO upper contacts,” IEEE J. Quantum Electron.39(11), 1439–1443 (2003). [CrossRef]
  38. Y. Z. Chiou, “Leakage current analysis of nitride-based photodetectors by emission microscopy inspection,” IEEE Sens. J.8(9), 1506–1510 (2008). [CrossRef]

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