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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 7 — Mar. 26, 2012
  • pp: 7575–7579
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Broadband and omnidirectional light harvesting enhancement of fluorescent SiC

Yiyu Ou, Valdas Jokubavicius, Philip Hens, Michl Kaiser, Peter Wellmann, Rositza Yakimova, Mikael Syväjärvi, and Haiyan Ou  »View Author Affiliations


Optics Express, Vol. 20, Issue 7, pp. 7575-7579 (2012)
http://dx.doi.org/10.1364/OE.20.007575


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Abstract

In the present work, antireflective sub-wavelength structures have been fabricated on fluorescent 6H-SiC to enhance the white light extraction efficiency by using the reactive-ion etching method. Broadband and omnidirectional antireflection characteristics show that 6H-SiC with antireflective sub-wavelength structures suppress the average surface reflection significantly from 20.5 % to 1.01 % over a wide spectral range of 390-784 nm. The luminescence intensity of the fluorescent 6H-SiC could be enhanced in the whole emission angle range. It maintains an enhancement larger than 91 % up to the incident angle of 70 degrees, while the largest enhancement of 115.4 % could be obtained at 16 degrees. The antireflective sub-wavelength structures on fluorescent 6H-SiC could also preserve the luminescence spectral profile at a large emission angle by eliminating the Fabry-Pérot microcavity interference effect.

© 2012 OSA

1. Introduction

White light-emitting diodes (LEDs) consisting of a nitride-based blue LED chip and phosphor are very promising candidates for the general lighting applications as energy-saving and environment friendly light sources [1

1. C. Shen, K. Li, Q. Hou, H. Feng, and X. Dong, “White LED based on YAG: Ce, Gd phosphor and CdSe-ZnS core/shell quantum dots,” IEEE Photon. Technol. Lett. 22, 884–886 (2010). [CrossRef]

5

5. H. Menkara, R. A. Gilstrap Jr., T. Morris, M. Minkara, B. K. Wagner, and C. J. Summers, “Development of nanophosphors for light emitting diodes,” Opt. Express 19, A972–A981 (2011). [CrossRef] [PubMed]

]. Recently, donor-acceptor doped fluorescent SiC has been proven as a highly efficient wavelength converter material much superior to the phosphors in terms of high color rendering index (CRI) value and long lifetime [6

6. S. Kamiyama, T. Maeda, Y. Nakamura, M. Iwaya, H. Amano, I. Akasaki, H. Kinoshita, T. Furusho, M. Yoshi-moto, T. Kimoto, J. Suda, A. Henry, I. G. Ivanov, J. P. Bergman, B. Monemar, T. Onuma, and S. F. Chichibu, “Extremely high quantum efficiency of donor-acceptor-pair emission in N-and-B-doped 6H-SiC,” J. Appl. Phys. 99, 093108 (2006). [CrossRef]

, 7

7. Y. Ou, V. Jokubavicius, S. Kamiyama, C. Liu, R. W. Berg, M. Linnarsson, R. Yakimova, M. Syväjärvi, and H. Ou, “Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC,” Opt. Mater. Express 1, 1439–1446 (2011). [CrossRef]

]. The donor-acceptor-pair (DAP) band luminescences from the nitrogen (N)-boron (B) doped 6H-SiC present a warm-white color. Combined with the DAP luminescences from the nitrogen-aluminium doped 6H-SiC, pure white light with CRI larger than 90 could be produced [8

8. S. Kamiyama, M. Iwaya, T. Takeuchi, I. Akasaki, M. Syväjärvi, and R. Yakimova, “Fluorescent SiC and its application to white light-emitting diodes,” J. Semicond. 32, 013004 (2011). [CrossRef]

, 9

9. Y. Ou, D. Corell, C. Dam-Hansen, P. Petersen, and H. Ou, “Antireflective sub-wavelength structures for improvement of the extraction efficiency and color rendering index of monolithic white light-emitting diode,” Opt. Express 19, A166–A172 (2011). [CrossRef] [PubMed]

]. Furthermore, SiC is a well-established substrate material for nitride growth and has an excellent thermal conductivity.

The light extraction efficiency of the SiC-based LED is usually low due to the internal re-flection loss arising from the large refractive index difference between the SiC and air interfaces. Antireflective sub-wavelength structures (ARS) have been proved as an ideal approach to enhance the light transmittance over a broad spectral bandwidth [10

10. Q. Chen, G. Hubbard, P. A. Shields, C. Liu, D. W. E. Allsopp, W. N. Wang, and S. Abbott, “Broadband moth-eye antireflection coatings fabricated by low-cost nanoimprinting,” Appl. Phys. Lett. 94, 263118 (2009). [CrossRef]

13

13. J. W. Leem, Y. M. Song, and J. S. Yu, “Broadband wide-angle antireflection enhancement in AZO/Si shell/core subwavelength grating structures with hydrophobic surface for Si-based solar cells,” Opt. Express 19, A1155–A1164 (2011). [CrossRef] [PubMed]

]. Applying the ARS on SiC has been studied on the monochromatic LEDs with undoped SiC as substrate materials [14

14. T. Seko, S. Mabuchi, F. Teramae, A. Suzuki, Y. Kaneko, R. Kawai, S. Kamiyama, M. Iwaya, H. Amano, and I. Akasaki, “Fabrication technique for moth-eye structure using low-energy electron-beam projection lithography for high-performance blue-lightemitting diode on SiC substrate,” Proc. SPIE 7216, 721628 (2009). [CrossRef]

, 15

15. R. Kawai, T. Kondo, A. Suzuki, F. Teramae, T. Kitano, K. Tamura, H. Sakurai, M. Iwaya, H. Amano, S. Kamiyama, I. Akasaki, M. Chen, A. Li, and K. Su, “Realization of extreme light extraction efficiency for moth-eye LEDs on SiC substrate using high-reflection electrode,” Phys. Status Solidi C 7, 2180–2182 (2010). [CrossRef]

] and on the 4H-SiC photodiodes [16

16. M. Kang, S. Joo, W. Bahng, J. Lee, N. Kim, and S. Koo, “Anti-reflective nano- and micro-structures on 4H-SiC for photodiodes,” Nanoscale Res. Lett. 6, 236 (2011). [CrossRef] [PubMed]

]. In the present work, the effect of ARS on the fluorescent SiC to enhance the light extraction efficiency over the entire visible spectral range has been studied.

2. Experiments

Homoepitaxial layers of 6H-SiC with N and B dopants were grown by the Fast Sublimation Growth Process [17

17. M. Syväjärvi and R. Yakimova, “Sublimation epitaxial growth of hexagonal and cubic SiC,” in Encyclopedia - the Comprehensive Semiconductor Science and Technology, P. Bhattacharya, R. Fornari, and H. Kamimura, eds. (Elsevier, 2011). [CrossRef]

]. The growth process is driven by a temperature gradient created between the source, in a form of polycrystalline SiC plate, and the substrate. Boron was introduced into the epilayers by doping from the source and nitrogen incorporation was controlled by adjusting the N2 gas pressure during the growth. The 6H-SiC epilayers were grown on 6H-SiC (0001) substrates with 1.4 degree off-orientation in the [112̅0] direction at growth temperature of 1725°C.

Here we present an approach to fabricate the periodic cone-shaped ARS on the N-B doped 6H-SiC by using the reactive-ion etching (RIE), and the fabrication process is illustrated in Fig. 1. Firstly, the positive e-beam resist (ZEP520) was spin-coated on the SiC sample (Fig. 1(a)) and then pre-baked on a hot plate at 160°C for 2 minutes (Fig. 1(b)). By using the e-beam lithography (JEOL JBX9300FS) with a subsequent development process, the designed pattern was transferred to the e-beam resist coating (Fig. 1(c)). A hard mask material (chromium) layer was then deposited on the patterned SiC by the e-beam evaporation (Fig. 1(d)). Followed by a lift-off process, the dot-shaped pattern of chromium was obtained as a hard mask layer (Fig. 1(e)). The dry etching process using SF6 and O2 precursors was carried out in the RIE system. During the etch process, the radio frequency power (100 W), process pressure (30 mT), and gas flow rates (20 sccm SF6, 5 sccm O2) of the RIE were carefully chosen. After 12 minutes etching, the cone-shaped ARS with designed configuration (bottom diameter of 240 nm, pitch of 340 nm, height of 1.2 μm, and hexagonal arrangement) were finally formed on the SiC surface (Fig. 1(f)). An oblique-view scanning electron microscope (SEM) figure of the SiC sample with ARS array is shown in Fig. 2(a).

Fig. 1 Schematic illustrations of the SiC ARS fabrication process steps (a)–(f).
Fig. 2 (a) An oblique-view SEM figure of the SiC sample with ARS, and (b) reflectance spectra of the SiC samples with and without ARS (measured at 6 deg.).

3. Characterization and results

The surface reflectance of the bare and ARS SiC samples were measured by a goniometer system at a measured angle of 6 degrees (deg.), where 0 deg. is the direction normal to the sample surface. The reflectance spectra were measured from 390 to 785 nm which covers the entire visible spectral range (typically from 390 to 750 nm) and the results are shown in Fig. 2(b). It is seen that the surface reflection is effectively suppressed by applying the SiC ARS. The average reflectance over the measured spectral range decreased from 20.5 % to 1.01 % and the minimum reflectance close to 0 was observed at around 400 nm for the ARS SiC sample. Although the reflectance starts to increase at above 680 nm, the reflectance over the entire visible spectral range is below 2 %. This result suggests that the SiC ARS is an effective way to suppress the surface reflection for the fluorescent SiC sample in the whole visible spectral range.

The angle-resolved room temperature photoluminescence spectra of the SiC samples with and without the ARS were also acquired by the same goniometer system. A 377 nm diode laser was used as the excitation source which was normal to the sample surface and the detected emission angle varied from 16 to 80 degrees. The broad DAP band luminescence of the N-B doped fluorescent SiC has a peak wavelength at round 578 nm and a full width at half maximum of 110 nm which is a merit as wavelength converter material. From Fig. 3(a), it is seen that the luminescence intensity of the bare SiC decreases together with a blue shift of the peak wavelength as the emission angle increases from 20 to 70 deg., which could be attributed to the Fabry-Pérot microcavity interference effect explained in the Ref. [7

7. Y. Ou, V. Jokubavicius, S. Kamiyama, C. Liu, R. W. Berg, M. Linnarsson, R. Yakimova, M. Syväjärvi, and H. Ou, “Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC,” Opt. Mater. Express 1, 1439–1446 (2011). [CrossRef]

, 18

18. D. Sotta, E. Hadji, N. Magnea, E. Delamadeleine, P. Besson, P. Renard, and H. Moriceau, “Resonant optical microcavity based on crystalline silicon active layer,” J. Appl. Phys. 92, 2207–2209 (2002). [CrossRef]

, 19

19. S. S. Pan, C. Ye, X. M. Teng, and G. H. Li, “Angle-dependent photoluminescence of [110]-oriented nitrogen-doped SnO2 films,” J. Phys. D: Appl. Phys. 40, 4771–4774 (2007). [CrossRef]

]. In Fig. 3(b), although the luminescence intensity of the ARS SiC also decreases with larger emission angle, the peak wavelength remains the same which is due to the elimination of the Fabry-Pérot microcavity interference effect by introducing the ARS on the SiC surface.

Fig. 3 Angle-resolved photoluminescence spectra from 20, 30, 40, 50, 60, to 70 deg. for the SiC samples (a) without and (b) with ARS; (c) integrated luminescence intensities and the (d) luminescence enhancement of the two SiC samples.

The integral luminescence intensities of the two samples at different emission angle are compared in Fig. 3(c). In both samples, the luminescence intensity at a large emission angle of 60 deg. is still higher than 52 % of the one at 16 deg., which is quite promising among the most commercial LEDs (less than 30 %). The angle-resolved luminescence enhancement of the ARS SiC is also shown in Fig. 3(d). It is seen that the luminescence intensity is enhanced by larger than 91 % from 16 to 70 deg., and the highest enhancement of 115.4 % is obtained at 16 deg. of the emission angle. Although the enhancement starts to decrease dramatically from 70 deg., the luminescence intensity of the SiC is significantly enhanced in a very large emission angle range.

4. Conclusion

A method by using reactive-ion etching is demonstrated to fabricate the ARS array on fluo-rescent SiC. The surface reflectance over the whole visible spectral range is dramatically suppressed from 20.5 % to 1.01 % by applying the ARS on the SiC sample. From the angle-resolved photoluminescence measurements, it is also found that the luminescence intensity could be enhanced by more than 91 % in a very large emission angle range (up to 70 degrees). In addition, the Fabry-Pérot microcavity interference effect could be eliminated to preserve the luminescence spectral profile by introducing the ARS on fluorescent SiC. As a result, broadband and omnidirectional ARS could effectively enhance the light extraction efficiency of the fluorescent SiC, and further improve the external quantum efficiency of the SiC-based white LEDs.

Acknowledgments

This work was supported by the Danish councils for strategic research funding (no. 09-072118), Swedish Energy Agency, Nordic Energy Research, Swedish Research Council (no. 2009-5307), Department of the New Energy and Industrial Technology Development Organization.

References and links

1.

C. Shen, K. Li, Q. Hou, H. Feng, and X. Dong, “White LED based on YAG: Ce, Gd phosphor and CdSe-ZnS core/shell quantum dots,” IEEE Photon. Technol. Lett. 22, 884–886 (2010). [CrossRef]

2.

C. Chang, C. Chen, C. Wu, S. Chang, J. Hung, and Y. Chi, “High-color-rendering pure-white phosphorescent organic light-emitting devices employing only two complementary colors,” Org. Electron. 11, 266–272 (2010). [CrossRef]

3.

R. Mueller-Mach, G. Mueller, M. R. Krames, H. A. Höppe, F. Stadler, W. Schnick, T. Juestel, and P. Schmidt, “Highly efficient all-nitride phosphor-converted white light emitting diode,” Phys. Status Solidi A 202, 1727–1732 (2005). [CrossRef]

4.

H. Kuo, C. Hung, H. Chen, K. Chen, C. Wang, C. Sher, C. Yeh, C. Lin, C. Chen, and Y. Cheng, “Patterned structure of remote phosphor for phosphor-converted white LEDs,” Opt. Express 19, A930–A936 (2011). [CrossRef] [PubMed]

5.

H. Menkara, R. A. Gilstrap Jr., T. Morris, M. Minkara, B. K. Wagner, and C. J. Summers, “Development of nanophosphors for light emitting diodes,” Opt. Express 19, A972–A981 (2011). [CrossRef] [PubMed]

6.

S. Kamiyama, T. Maeda, Y. Nakamura, M. Iwaya, H. Amano, I. Akasaki, H. Kinoshita, T. Furusho, M. Yoshi-moto, T. Kimoto, J. Suda, A. Henry, I. G. Ivanov, J. P. Bergman, B. Monemar, T. Onuma, and S. F. Chichibu, “Extremely high quantum efficiency of donor-acceptor-pair emission in N-and-B-doped 6H-SiC,” J. Appl. Phys. 99, 093108 (2006). [CrossRef]

7.

Y. Ou, V. Jokubavicius, S. Kamiyama, C. Liu, R. W. Berg, M. Linnarsson, R. Yakimova, M. Syväjärvi, and H. Ou, “Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC,” Opt. Mater. Express 1, 1439–1446 (2011). [CrossRef]

8.

S. Kamiyama, M. Iwaya, T. Takeuchi, I. Akasaki, M. Syväjärvi, and R. Yakimova, “Fluorescent SiC and its application to white light-emitting diodes,” J. Semicond. 32, 013004 (2011). [CrossRef]

9.

Y. Ou, D. Corell, C. Dam-Hansen, P. Petersen, and H. Ou, “Antireflective sub-wavelength structures for improvement of the extraction efficiency and color rendering index of monolithic white light-emitting diode,” Opt. Express 19, A166–A172 (2011). [CrossRef] [PubMed]

10.

Q. Chen, G. Hubbard, P. A. Shields, C. Liu, D. W. E. Allsopp, W. N. Wang, and S. Abbott, “Broadband moth-eye antireflection coatings fabricated by low-cost nanoimprinting,” Appl. Phys. Lett. 94, 263118 (2009). [CrossRef]

11.

L. Sainiemi, V. Jokinen, A. Shah, M. Shpak, S. Aura, P. Suvanto, and S. Franssila, “Non-reflcecting silicon and polymer surfaces by plasma etching and replication,” Adv. Mater. 23, 122–126 (2011). [CrossRef]

12.

N. Yamada, T. Ijiro, E. Okamoto, K. Hayashi, and H. Masuda, “Characterization of antireflection moth-eye film on crystalline silicon photovoltaic module,” Opt. Express 19, A118–A125 (2011). [CrossRef] [PubMed]

13.

J. W. Leem, Y. M. Song, and J. S. Yu, “Broadband wide-angle antireflection enhancement in AZO/Si shell/core subwavelength grating structures with hydrophobic surface for Si-based solar cells,” Opt. Express 19, A1155–A1164 (2011). [CrossRef] [PubMed]

14.

T. Seko, S. Mabuchi, F. Teramae, A. Suzuki, Y. Kaneko, R. Kawai, S. Kamiyama, M. Iwaya, H. Amano, and I. Akasaki, “Fabrication technique for moth-eye structure using low-energy electron-beam projection lithography for high-performance blue-lightemitting diode on SiC substrate,” Proc. SPIE 7216, 721628 (2009). [CrossRef]

15.

R. Kawai, T. Kondo, A. Suzuki, F. Teramae, T. Kitano, K. Tamura, H. Sakurai, M. Iwaya, H. Amano, S. Kamiyama, I. Akasaki, M. Chen, A. Li, and K. Su, “Realization of extreme light extraction efficiency for moth-eye LEDs on SiC substrate using high-reflection electrode,” Phys. Status Solidi C 7, 2180–2182 (2010). [CrossRef]

16.

M. Kang, S. Joo, W. Bahng, J. Lee, N. Kim, and S. Koo, “Anti-reflective nano- and micro-structures on 4H-SiC for photodiodes,” Nanoscale Res. Lett. 6, 236 (2011). [CrossRef] [PubMed]

17.

M. Syväjärvi and R. Yakimova, “Sublimation epitaxial growth of hexagonal and cubic SiC,” in Encyclopedia - the Comprehensive Semiconductor Science and Technology, P. Bhattacharya, R. Fornari, and H. Kamimura, eds. (Elsevier, 2011). [CrossRef]

18.

D. Sotta, E. Hadji, N. Magnea, E. Delamadeleine, P. Besson, P. Renard, and H. Moriceau, “Resonant optical microcavity based on crystalline silicon active layer,” J. Appl. Phys. 92, 2207–2209 (2002). [CrossRef]

19.

S. S. Pan, C. Ye, X. M. Teng, and G. H. Li, “Angle-dependent photoluminescence of [110]-oriented nitrogen-doped SnO2 films,” J. Phys. D: Appl. Phys. 40, 4771–4774 (2007). [CrossRef]

OCIS Codes
(250.5230) Optoelectronics : Photoluminescence
(220.4241) Optical design and fabrication : Nanostructure fabrication
(310.6628) Thin films : Subwavelength structures, nanostructures

ToC Category:
Thin Films

History
Original Manuscript: January 24, 2012
Revised Manuscript: March 2, 2012
Manuscript Accepted: March 14, 2012
Published: March 19, 2012

Citation
Yiyu Ou, Valdas Jokubavicius, Philip Hens, Michl Kaiser, Peter Wellmann, Rositza Yakimova, Mikael Syväjärvi, and Haiyan Ou, "Broadband and omnidirectional light harvesting enhancement of fluorescent SiC," Opt. Express 20, 7575-7579 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-7-7575


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References

  1. C. Shen, K. Li, Q. Hou, H. Feng, X. Dong, “White LED based on YAG: Ce, Gd phosphor and CdSe-ZnS core/shell quantum dots,” IEEE Photon. Technol. Lett. 22, 884–886 (2010). [CrossRef]
  2. C. Chang, C. Chen, C. Wu, S. Chang, J. Hung, Y. Chi, “High-color-rendering pure-white phosphorescent organic light-emitting devices employing only two complementary colors,” Org. Electron. 11, 266–272 (2010). [CrossRef]
  3. R. Mueller-Mach, G. Mueller, M. R. Krames, H. A. Höppe, F. Stadler, W. Schnick, T. Juestel, P. Schmidt, “Highly efficient all-nitride phosphor-converted white light emitting diode,” Phys. Status Solidi A 202, 1727–1732 (2005). [CrossRef]
  4. H. Kuo, C. Hung, H. Chen, K. Chen, C. Wang, C. Sher, C. Yeh, C. Lin, C. Chen, Y. Cheng, “Patterned structure of remote phosphor for phosphor-converted white LEDs,” Opt. Express 19, A930–A936 (2011). [CrossRef] [PubMed]
  5. H. Menkara, R. A. Gilstrap, T. Morris, M. Minkara, B. K. Wagner, C. J. Summers, “Development of nanophosphors for light emitting diodes,” Opt. Express 19, A972–A981 (2011). [CrossRef] [PubMed]
  6. S. Kamiyama, T. Maeda, Y. Nakamura, M. Iwaya, H. Amano, I. Akasaki, H. Kinoshita, T. Furusho, M. Yoshi-moto, T. Kimoto, J. Suda, A. Henry, I. G. Ivanov, J. P. Bergman, B. Monemar, T. Onuma, S. F. Chichibu, “Extremely high quantum efficiency of donor-acceptor-pair emission in N-and-B-doped 6H-SiC,” J. Appl. Phys. 99, 093108 (2006). [CrossRef]
  7. Y. Ou, V. Jokubavicius, S. Kamiyama, C. Liu, R. W. Berg, M. Linnarsson, R. Yakimova, M. Syväjärvi, H. Ou, “Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC,” Opt. Mater. Express 1, 1439–1446 (2011). [CrossRef]
  8. S. Kamiyama, M. Iwaya, T. Takeuchi, I. Akasaki, M. Syväjärvi, R. Yakimova, “Fluorescent SiC and its application to white light-emitting diodes,” J. Semicond. 32, 013004 (2011). [CrossRef]
  9. Y. Ou, D. Corell, C. Dam-Hansen, P. Petersen, H. Ou, “Antireflective sub-wavelength structures for improvement of the extraction efficiency and color rendering index of monolithic white light-emitting diode,” Opt. Express 19, A166–A172 (2011). [CrossRef] [PubMed]
  10. Q. Chen, G. Hubbard, P. A. Shields, C. Liu, D. W. E. Allsopp, W. N. Wang, S. Abbott, “Broadband moth-eye antireflection coatings fabricated by low-cost nanoimprinting,” Appl. Phys. Lett. 94, 263118 (2009). [CrossRef]
  11. L. Sainiemi, V. Jokinen, A. Shah, M. Shpak, S. Aura, P. Suvanto, S. Franssila, “Non-reflcecting silicon and polymer surfaces by plasma etching and replication,” Adv. Mater. 23, 122–126 (2011). [CrossRef]
  12. N. Yamada, T. Ijiro, E. Okamoto, K. Hayashi, H. Masuda, “Characterization of antireflection moth-eye film on crystalline silicon photovoltaic module,” Opt. Express 19, A118–A125 (2011). [CrossRef] [PubMed]
  13. J. W. Leem, Y. M. Song, J. S. Yu, “Broadband wide-angle antireflection enhancement in AZO/Si shell/core subwavelength grating structures with hydrophobic surface for Si-based solar cells,” Opt. Express 19, A1155–A1164 (2011). [CrossRef] [PubMed]
  14. T. Seko, S. Mabuchi, F. Teramae, A. Suzuki, Y. Kaneko, R. Kawai, S. Kamiyama, M. Iwaya, H. Amano, I. Akasaki, “Fabrication technique for moth-eye structure using low-energy electron-beam projection lithography for high-performance blue-lightemitting diode on SiC substrate,” Proc. SPIE 7216, 721628 (2009). [CrossRef]
  15. R. Kawai, T. Kondo, A. Suzuki, F. Teramae, T. Kitano, K. Tamura, H. Sakurai, M. Iwaya, H. Amano, S. Kamiyama, I. Akasaki, M. Chen, A. Li, K. Su, “Realization of extreme light extraction efficiency for moth-eye LEDs on SiC substrate using high-reflection electrode,” Phys. Status Solidi C 7, 2180–2182 (2010). [CrossRef]
  16. M. Kang, S. Joo, W. Bahng, J. Lee, N. Kim, S. Koo, “Anti-reflective nano- and micro-structures on 4H-SiC for photodiodes,” Nanoscale Res. Lett. 6, 236 (2011). [CrossRef] [PubMed]
  17. M. Syväjärvi, R. Yakimova, “Sublimation epitaxial growth of hexagonal and cubic SiC,” in Encyclopedia - the Comprehensive Semiconductor Science and Technology, P. Bhattacharya, R. Fornari, H. Kamimura, eds. (Elsevier, 2011). [CrossRef]
  18. D. Sotta, E. Hadji, N. Magnea, E. Delamadeleine, P. Besson, P. Renard, H. Moriceau, “Resonant optical microcavity based on crystalline silicon active layer,” J. Appl. Phys. 92, 2207–2209 (2002). [CrossRef]
  19. S. S. Pan, C. Ye, X. M. Teng, G. H. Li, “Angle-dependent photoluminescence of [110]-oriented nitrogen-doped SnO2 films,” J. Phys. D: Appl. Phys. 40, 4771–4774 (2007). [CrossRef]

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