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Optical Materials Express

Optical Materials Express

  • Editor: David J. Hagan
  • Vol. 1, Iss. 3 — Jul. 1, 2011
  • pp: 451–457
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Highly tolerant a-Si distributed Bragg reflector fabricated by oblique angle deposition

Sung Jun Jang, Young Min Song, Chan Il Yeo, Chang Young Park, and Yong Tak Lee  »View Author Affiliations


Optical Materials Express, Vol. 1, Issue 3, pp. 451-457 (2011)
http://dx.doi.org/10.1364/OME.1.000451


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Abstract

We demonstrate a highly tolerant and highly reflective broadband a-Si distributed Bragg reflector fabricated by oblique angle deposition. By tuning the refractive index of an a-Si film, a high index contrast material system was achieved. The highly tolerant and broadband reflective characteristics of the a-Si distributed Bragg reflector were investigated by calculation and fabrication. A broad stop band (Δλ/λ = 33.7%, R>99%) with only a five-pair a-Si distributed Bragg reflector was achieved experimentally. The size-, feature- and substrate-independent method for highly reflective Bragg reflectors was realized by simple oblique angle evaporation.

© 2011 OSA

1. Introduction

Broadband high reflective distributed Bragg reflectors (DBRs) are essential in optical devices, including telecommunication, semiconductor lasers, solar cells, optical sensors, and photo detectors [1

1. M. C. Y. Huang, Y. Zhou, and C. J. Chang-hasnain, “A surface-emitting laser incorporating a high-index-contrast subwavelength grating,” Nat. Photonics 1(2), 119–122 (2007). [CrossRef]

4

4. S. N. Tandon, J. T. Gopinath, H. M. Shen, G. S. Petrich, L. A. Kolodziejski, F. X. Kärtner, and E. P. Ippen, “Large-area broadband saturable Bragg reflectors by use of oxidized AlAs,” Opt. Lett. 29(21), 2551–2553 (2004). [CrossRef] [PubMed]

]. For DBRs, the reflectivity and stop band width directly depend on the refractive index contrast between the high- and low-index material, i.e., a higher refractive index contrast contributes to a higher reflectivity and a wider stop band. Moreover, a higher index contrast guarantees higher tolerance during the fabrication process of DBRs in the cases of permissible deviation of stop band width. Because process parameters such as the deposition rate seriously affect the quality of thin film optical components, highly tolerant DBRs are prerequisite to low-cost fabrication. Thus far, various material systems or novel techniques have been used to realize broadband high-reflective DBRs; however, these have their own limitations, including, 1) the necessity for expensive equipment and a substrate-sensitive process, 2) a complicated and protracted process, 3) non-conductive and poor thermal properties, and 4) low refractive index contrast [5

5. J. Boucart, C. Starck, F. Gaborit, A. Plais, N. Bouche, E. Derouin, J. C. Remy, J. Bonnet-Gamard, L. Goldstein, C. Fortin, D. Carpentier, P. Salet, F. Brillouet, and J. Jacquet, “Metamorphic DBR and tunnel-junction injection: A CW RT monolithic long-wavelength VCSEL,” IEEE J. Sel. Top. Quantum Electron. 5(3), 520–529 (1999). [CrossRef]

8

8. Y. H. Lin, C. L. Wu, Y. H. Pai, and G. R. Lin, “A 533-nm self-luminescent Si-rich SiNx/SiOx distributed Bragg reflector,” Opt. Express 19(7), 6563–6570 (2011). [CrossRef] [PubMed]

]. Moreover, these material systems are heterostructures, as DBRs generally consist of several pairs of different materials with different refractive indices. However, the refractive index and other properties of this type of material, such as conductivity and thermal expansion coefficient are in general inseparably coupled. Due to the limited number of available materials, the choice of the refractive index also dictates the remaining material characteristics. Although porous silicon multilayers were reported in the early 1990s for a homogeneous material system, it has been limited by process tolerances, e.g. etch rate and process temperature [9

9. G. Zalczer, O. Thomas, J. P. Piel, and J. L. Stehle, “IR spectroscopic ellipsometry: instrumentation and applications in semiconductors,” Thin Solid Films 234(1-2), 356–362 (1993). [CrossRef]

,10

10. C. Mazzoleni and L. Pavesi, “Application to optical components of dielectric porous silicon multilayers,” Appl. Phys. Lett. 67(20), 2983–2985 (1995). [CrossRef]

].

Recently, it was shown that oblique-angle deposition (OAD) of materials, e.g., SiO2, TiO2 and ITO, can be used to fabricate optical components with optical properties that can be controlled by the oblique angle [11

11. M. J. Brett and M. M. Hawkeye, “Materials science. New materials at a glance,” Science 319(5867), 1192–1193 (2008). [CrossRef] [PubMed]

13

13. J. K. Kim, T. Gessmann, E. F. Schubert, J. Q. Xi, H. Luo, J. Cho, C. Sone, and Y. Park, “GaInN light-emitting diode with conductive omnidirectional reflector having a low-refractive-index indium-tin oxide layer,” Appl. Phys. Lett. 88(1), 013501 (2006). [CrossRef]

]. By controlling the angle of deposition and thereby the layer porosity and refractive index, oblique-angle deposition allows the fabrication of thin film optical components composed of a single material chosen for its optical properties in which each layer has a different refractive index that is individually tuned to a specific desired value. Schubert et al. reported experimental results involving a homogeneous DBR structure by OAD but the index contrast was still low [14

14. M. F. Schubert, J. Q. Xi, J. K. Kim, and E. F. Schubert, “Distributed Bragg reflector consisting of high- and low-refractive-index thin film layers made of the same material,” Appl. Phys. Lett. 90(14), 141115 (2007). [CrossRef]

]. The capability of the use of a single-step and single-material deposition for high-low or graded-index optical component is crucial when a highly tolerant process is important [15

15. M. M. Hawkeye and M. J. Brett, “Narrow bandpass optical filters fabricated with one-dimensionally periodic inhomogeneous thin films,” J. Appl. Phys. 100(4), 044322 (2006). [CrossRef]

].

This paper represents the first-demonstration of amorphous silicon (a-Si) DBRs fabricated by OAD having high process tolerance and broadband high-reflective properties due to the high index contrast. A five-period a-Si/a-Si DBR was fabricated by OAD via e-beam evaporation on a two-inch silicon wafer (100). The reflectivity and wafer-scale uniformity were analyzed by spectrophotometry measurements and reflectivity mapping. This a-Si/a-Si DBR has advantages in that it offers the least complicated means of realizing a highly tolerant and large-scale mirror fabrication process leading to high reflectivity with a wide stop band.

2. Design and Fabrication

3. Results and Discussion

To demonstrate the high process tolerance and potential for a large-scale process, we fabricated a 2” full-wafer a-Si/a-Si DBR with five periods. The result from the reflectivity mapping of the 2” full-wafer a-Si/a-Si DBR is shown in Fig. 4 (a)
Fig. 4 (a) The relative reflectance mapping image of 2” full-wafer DBR fabricated on Si substrate. The words, A-E, represent each measurement position for the reflectivity. (b) The measured reflectivity of all positions of DBR fabricated on 2” Si wafer as a function of wavelength.
. The relative reflectivity map was measured by reflectance mapping tool (RPM 2000, Nanometrics) at the center wavelength of 1550 nm. There is a slightly different color in the measured relative reflectivity, as the wafer was not rotated in the evaporating chamber. This indicates that the evaporating distance to one edge of the wafer is slightly different from the distance to the opposite edge. Nevertheless, relatively uniform reflectivity of the full-wafer DBR was achieved. To study the influence of the sample position on the reflectivity, we measured the reflectivity of each position marked in Fig. 4 (a) by spectrophotometry measurement. As shown in Fig. 4 (b), there was little difference in the measured reflectivity of each position. Furthermore, the calculated results shown in Fig. 5
Fig. 5 Calculated reflectivity spectra and thickness deviation dependency of the five-period a-Si/a-Si DBR as a function of wavelength.
show that a certain amount of thickness deviation does not have a serious effect on the reflectivity of the a-Si/a-Si DBR at the target wavelength. This is also true for the circumferential wavelength. In Fig. 4 (b), the largest difference exists between B and E. The wavelength difference of spectral band width between B and E was about 45 nm. We can define the thickness errors of position B and E from Fig. 5. They were −5 nm and −1 nm respectively, and the total deviation across the whole wafer was only 4 nm. Therefore, the DBRs oblique angle deposited on 2” wafer show relatively good uniformity. Therefore, we can indeed confirm that the highly tolerant and high reflective a-Si/a-Si DBR is useful, practical and innovative for cost-effective optical components capable of high levels of reflection.

Figure 6 (a)
Fig. 6 (a) Photographic image of ‘GIST’-patterned a-Si/a-Si DBR on Si substrate. (b) Relative reflectance mapping image of ‘GIST’-patterned a-Si/a-Si DBR on Si substrate.
shows a digital photographic image of the deposited a-Si/a-Si DBR shaped as the media mark of an institute. Any size or any feature of a structure can be fabricated by a simple lift-off process for the realization of a highly reflective broadband DBR suitable for various optoelectronic devices. As shown in Fig. 6 (b), the relative reflectivity of the patterned structure at 1550 nm was plainly higher than that of a normal Si (100) substrate and the superiority of the tolerant a-Si/a-Si DBR and its fabrication process are clearly evident.

4. Conclusion

In summary, we proposed a novel class of DBRs based the OAD of a-Si. The reflective characteristics were investigated both theoretically and experimentally. Highly tolerant and highly reflective broadband a-Si/a-Si DBRs were demonstrated successfully for the first time. A broadband stop band (Δλ/λ = 33.7%, R>99%) with only a five-period a-Si/a-Si DBR was achieved experimentally. The size-, feature- and substrate-independent method to realize highly tolerant and broadband DBRs will provide an interesting new pathway that opens future practical applications such as resonant-cavity-light-emitting-diodes or vertical-cavity-surface-emitting-lasers or solar cells. In an addition, oblique-angle deposition is promising for the growth of homogeneous highly reflective DBR structures with a very high refractive index contrast.

Acknowledgments

This work was partially supported by the “Systems biology infrastructure establishment grant” provided by GIST in 2011 and by the WCU program of MEST (Project No. R31-2008-000-10026-0) and by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2011-0017606).

References and links

1.

M. C. Y. Huang, Y. Zhou, and C. J. Chang-hasnain, “A surface-emitting laser incorporating a high-index-contrast subwavelength grating,” Nat. Photonics 1(2), 119–122 (2007). [CrossRef]

2.

L. Zeng, P. Bermel, Y. Yi, B. A. Alamariu, K. A. Broderick, J. Liu, C. Hong, X. Duan, J. Joannopoulos, and L. C. Kimerling, “Demonstration of enhanced absorption in thin film Si solar cells with textured photonic crystal back reflector,” Appl. Phys. Lett. 93(22), 221105 (2008). [CrossRef]

3.

M. J. Thorpe, K. D. Moll, R. J. Jones, B. Safdi, and J. Ye, “Broadband cavity ringdown spectroscopy for sensitive and rapid molecular detection,” Science 311(5767), 1595–1599 (2006). [CrossRef] [PubMed]

4.

S. N. Tandon, J. T. Gopinath, H. M. Shen, G. S. Petrich, L. A. Kolodziejski, F. X. Kärtner, and E. P. Ippen, “Large-area broadband saturable Bragg reflectors by use of oxidized AlAs,” Opt. Lett. 29(21), 2551–2553 (2004). [CrossRef] [PubMed]

5.

J. Boucart, C. Starck, F. Gaborit, A. Plais, N. Bouche, E. Derouin, J. C. Remy, J. Bonnet-Gamard, L. Goldstein, C. Fortin, D. Carpentier, P. Salet, F. Brillouet, and J. Jacquet, “Metamorphic DBR and tunnel-junction injection: A CW RT monolithic long-wavelength VCSEL,” IEEE J. Sel. Top. Quantum Electron. 5(3), 520–529 (1999). [CrossRef]

6.

D. J. Ripin, J. T. Gopinath, H. M. Shen, A. A. Erchak, G. S. Petrich, L. A. Kolodziejski, F. X. Kartner, and E. P. Ippen, “Oxidized GaAs/AlAs mirror with a quantum-well saturable absorber for ultrashort-pulse Cr4+:YAG laser,” Opt. Commun. 214(1-6), 285–289 (2002). [CrossRef]

7.

E. F. Schubert, N. E. J. Hunt, A. M. Vredenberg, T. D. Harris, J. M. Poate, D. C. Jacobson, Y. H. Wong, and G. J. Zydzik, “Enhanced photoluminescence by resonant absorption in Er-doped SiO2/Si microcavities,” Appl. Phys. Lett. 63(19), 2603–2605 (1993). [CrossRef]

8.

Y. H. Lin, C. L. Wu, Y. H. Pai, and G. R. Lin, “A 533-nm self-luminescent Si-rich SiNx/SiOx distributed Bragg reflector,” Opt. Express 19(7), 6563–6570 (2011). [CrossRef] [PubMed]

9.

G. Zalczer, O. Thomas, J. P. Piel, and J. L. Stehle, “IR spectroscopic ellipsometry: instrumentation and applications in semiconductors,” Thin Solid Films 234(1-2), 356–362 (1993). [CrossRef]

10.

C. Mazzoleni and L. Pavesi, “Application to optical components of dielectric porous silicon multilayers,” Appl. Phys. Lett. 67(20), 2983–2985 (1995). [CrossRef]

11.

M. J. Brett and M. M. Hawkeye, “Materials science. New materials at a glance,” Science 319(5867), 1192–1193 (2008). [CrossRef] [PubMed]

12.

J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu, and J. A. Smart, “Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection,” Nat. Photonics 1, 176–179 (2007).

13.

J. K. Kim, T. Gessmann, E. F. Schubert, J. Q. Xi, H. Luo, J. Cho, C. Sone, and Y. Park, “GaInN light-emitting diode with conductive omnidirectional reflector having a low-refractive-index indium-tin oxide layer,” Appl. Phys. Lett. 88(1), 013501 (2006). [CrossRef]

14.

M. F. Schubert, J. Q. Xi, J. K. Kim, and E. F. Schubert, “Distributed Bragg reflector consisting of high- and low-refractive-index thin film layers made of the same material,” Appl. Phys. Lett. 90(14), 141115 (2007). [CrossRef]

15.

M. M. Hawkeye and M. J. Brett, “Narrow bandpass optical filters fabricated with one-dimensionally periodic inhomogeneous thin films,” J. Appl. Phys. 100(4), 044322 (2006). [CrossRef]

16.

Y. Zhong, Y. C. Shin, C. M. Kim, B. G. Lee, E. H. Kim, Y. J. Park, K. M. A. Sobahan, C. K. Hwangbo, Y. P. Lee, and T. G. Kim, “Optical and electrical properties of indium tin oxide thin films with tilted and spiral microstructures prepared by oblique angle deposition,” J. Mater. Res. 23(09), 2500–2505 (2008). [CrossRef]

17.

K. Robbie and M. J. Brett, “Sculptured thin films and glancing angle deposition: Growth mechanics and applications,” J. Vac. Sci. Technol. A 15(3), 1460–1465 (1997). [CrossRef]

18.

S. J. Jang, Y. M. Song, H. J. Choi, J. S. Yu, and Y. T. Lee, “Structural and optical properties of silicon by tilted angle evaporation,” Surf. Coat. Tech. 205, S447–S450 (2010). [CrossRef]

19.

O. Bisi, S. Ossicini, and L. Pavesi, “Porous silicon: a quantum sponge structure for silicon based optoelectronics,” Surf. Sci. Rep. 38(1-3), 1–126 (2000). [CrossRef]

20.

J. P. Singh, T. Karabacak, D.-X. Ye, D.-L. Liu, C. Picu, T.-M. Lu, and G.-C. Wang, “Physical properties of nanostructures grown by oblique angle deposition,” J. Vac. Sci. Technol. B 23(5), 2114–2121 (2005). [CrossRef]

21.

Y. M. Song, H. J. Choi, J. S. Yu, and Y. T. Lee, “Design of highly transparent glasses with broadband antireflective subwavelength structures,” Opt. Express 18(12), 13063–13071 (2010). [CrossRef] [PubMed]

22.

S. Chhajed, M. F. Schubert, J. K. Kim, and E. F. Schubert, “Nanostructured multilayer graded-index antireflection coating for Si solar cells with broadband and omnidirectional characteristics,” Appl. Phys. Lett. 93(25), 251108 (2008). [CrossRef]

23.

J. Fan, J. Fu, A. Collins, and Y. Zhao, “The effect of the shape of nanorod arrays on the nanocarpet effect,” Nanotechnology 19(4), 045713–045721 (2008). [CrossRef]

24.

S. J. Jang, Y. M. Song, J. S. Yu, C. I. Yeo, and Y. T. Lee, “Antireflective properties of porous Si nanocolumnar structures with graded refractive index layers,” Opt. Lett. 36(2), 253–255 (2011). [CrossRef] [PubMed]

25.

S. J. Jang, Y. M. Song, C. I. Yeo, C. Y. Park, J. S. Yu, and Y. T. Lee, “Antireflective property of thin film a-Si solar cell structures with graded refractive index structure,” Opt. Express 19(S2Suppl 2), A108–A117 (2011). [CrossRef] [PubMed]

26.

C. F. R. Mateus, M. C. Y. Huang, L. Chen, C. J. Chang-Hasnain, and Y. Suzuki, “Broad-band mirror (1.12-1.62 µm) using a subwavelength grating,” IEEE Photon. Technol. Lett. 16(7), 1676–1678 (2004). [CrossRef]

27.

L. Zeng, Y. Yi, C. Hong, J. Liu, N. Feng, X. Duan, L. C. Kimerling, and B. A. Alamariu, “Efficiency enhancement in Si solar cells by textured photonic crystal back reflector,” Appl. Phys. Lett. 89(11), 111111 (2006). [CrossRef]

28.

O. Blum, I. J. Fritz, L. R. Dawson, A. J. Howard, T. J. Headley, J. F. Klem, and T. J. Drummond, “Highly reflective, long wavelength AlAsSb/GaAsSb distributed Bragg reflector grown by molecular beam epitaxy on InP substrate,” Appl. Phys. Lett. 66(3), 329–331 (1995). [CrossRef]

OCIS Codes
(230.1480) Optical devices : Bragg reflectors
(310.1860) Thin films : Deposition and fabrication
(310.4165) Thin films : Multilayer design
(220.4241) Optical design and fabrication : Nanostructure fabrication

ToC Category:
Thin Films

History
Original Manuscript: April 20, 2011
Revised Manuscript: June 16, 2011
Manuscript Accepted: June 22, 2011
Published: June 24, 2011

Citation
Sung Jun Jang, Young Min Song, Chan Il Yeo, Chang Young Park, and Yong Tak Lee, "Highly tolerant a-Si distributed Bragg reflector fabricated by oblique angle deposition," Opt. Mater. Express 1, 451-457 (2011)
http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-1-3-451


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References

  1. M. C. Y. Huang, Y. Zhou, and C. J. Chang-hasnain, “A surface-emitting laser incorporating a high-index-contrast subwavelength grating,” Nat. Photonics 1(2), 119–122 (2007). [CrossRef]
  2. L. Zeng, P. Bermel, Y. Yi, B. A. Alamariu, K. A. Broderick, J. Liu, C. Hong, X. Duan, J. Joannopoulos, and L. C. Kimerling, “Demonstration of enhanced absorption in thin film Si solar cells with textured photonic crystal back reflector,” Appl. Phys. Lett. 93(22), 221105 (2008). [CrossRef]
  3. M. J. Thorpe, K. D. Moll, R. J. Jones, B. Safdi, and J. Ye, “Broadband cavity ringdown spectroscopy for sensitive and rapid molecular detection,” Science 311(5767), 1595–1599 (2006). [CrossRef] [PubMed]
  4. S. N. Tandon, J. T. Gopinath, H. M. Shen, G. S. Petrich, L. A. Kolodziejski, F. X. Kärtner, and E. P. Ippen, “Large-area broadband saturable Bragg reflectors by use of oxidized AlAs,” Opt. Lett. 29(21), 2551–2553 (2004). [CrossRef] [PubMed]
  5. J. Boucart, C. Starck, F. Gaborit, A. Plais, N. Bouche, E. Derouin, J. C. Remy, J. Bonnet-Gamard, L. Goldstein, C. Fortin, D. Carpentier, P. Salet, F. Brillouet, and J. Jacquet, “Metamorphic DBR and tunnel-junction injection: A CW RT monolithic long-wavelength VCSEL,” IEEE J. Sel. Top. Quantum Electron. 5(3), 520–529 (1999). [CrossRef]
  6. D. J. Ripin, J. T. Gopinath, H. M. Shen, A. A. Erchak, G. S. Petrich, L. A. Kolodziejski, F. X. Kartner, and E. P. Ippen, “Oxidized GaAs/AlAs mirror with a quantum-well saturable absorber for ultrashort-pulse Cr4+:YAG laser,” Opt. Commun. 214(1-6), 285–289 (2002). [CrossRef]
  7. E. F. Schubert, N. E. J. Hunt, A. M. Vredenberg, T. D. Harris, J. M. Poate, D. C. Jacobson, Y. H. Wong, and G. J. Zydzik, “Enhanced photoluminescence by resonant absorption in Er-doped SiO2/Si microcavities,” Appl. Phys. Lett. 63(19), 2603–2605 (1993). [CrossRef]
  8. Y. H. Lin, C. L. Wu, Y. H. Pai, and G. R. Lin, “A 533-nm self-luminescent Si-rich SiNx/SiOx distributed Bragg reflector,” Opt. Express 19(7), 6563–6570 (2011). [CrossRef] [PubMed]
  9. G. Zalczer, O. Thomas, J. P. Piel, and J. L. Stehle, “IR spectroscopic ellipsometry: instrumentation and applications in semiconductors,” Thin Solid Films 234(1-2), 356–362 (1993). [CrossRef]
  10. C. Mazzoleni and L. Pavesi, “Application to optical components of dielectric porous silicon multilayers,” Appl. Phys. Lett. 67(20), 2983–2985 (1995). [CrossRef]
  11. M. J. Brett and M. M. Hawkeye, “Materials science. New materials at a glance,” Science 319(5867), 1192–1193 (2008). [CrossRef] [PubMed]
  12. J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu, and J. A. Smart, “Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection,” Nat. Photonics 1, 176–179 (2007).
  13. J. K. Kim, T. Gessmann, E. F. Schubert, J. Q. Xi, H. Luo, J. Cho, C. Sone, and Y. Park, “GaInN light-emitting diode with conductive omnidirectional reflector having a low-refractive-index indium-tin oxide layer,” Appl. Phys. Lett. 88(1), 013501 (2006). [CrossRef]
  14. M. F. Schubert, J. Q. Xi, J. K. Kim, and E. F. Schubert, “Distributed Bragg reflector consisting of high- and low-refractive-index thin film layers made of the same material,” Appl. Phys. Lett. 90(14), 141115 (2007). [CrossRef]
  15. M. M. Hawkeye and M. J. Brett, “Narrow bandpass optical filters fabricated with one-dimensionally periodic inhomogeneous thin films,” J. Appl. Phys. 100(4), 044322 (2006). [CrossRef]
  16. Y. Zhong, Y. C. Shin, C. M. Kim, B. G. Lee, E. H. Kim, Y. J. Park, K. M. A. Sobahan, C. K. Hwangbo, Y. P. Lee, and T. G. Kim, “Optical and electrical properties of indium tin oxide thin films with tilted and spiral microstructures prepared by oblique angle deposition,” J. Mater. Res. 23(09), 2500–2505 (2008). [CrossRef]
  17. K. Robbie and M. J. Brett, “Sculptured thin films and glancing angle deposition: Growth mechanics and applications,” J. Vac. Sci. Technol. A 15(3), 1460–1465 (1997). [CrossRef]
  18. S. J. Jang, Y. M. Song, H. J. Choi, J. S. Yu, and Y. T. Lee, “Structural and optical properties of silicon by tilted angle evaporation,” Surf. Coat. Tech. 205, S447–S450 (2010). [CrossRef]
  19. O. Bisi, S. Ossicini, and L. Pavesi, “Porous silicon: a quantum sponge structure for silicon based optoelectronics,” Surf. Sci. Rep. 38(1-3), 1–126 (2000). [CrossRef]
  20. J. P. Singh, T. Karabacak, D.-X. Ye, D.-L. Liu, C. Picu, T.-M. Lu, and G.-C. Wang, “Physical properties of nanostructures grown by oblique angle deposition,” J. Vac. Sci. Technol. B 23(5), 2114–2121 (2005). [CrossRef]
  21. Y. M. Song, H. J. Choi, J. S. Yu, and Y. T. Lee, “Design of highly transparent glasses with broadband antireflective subwavelength structures,” Opt. Express 18(12), 13063–13071 (2010). [CrossRef] [PubMed]
  22. S. Chhajed, M. F. Schubert, J. K. Kim, and E. F. Schubert, “Nanostructured multilayer graded-index antireflection coating for Si solar cells with broadband and omnidirectional characteristics,” Appl. Phys. Lett. 93(25), 251108 (2008). [CrossRef]
  23. J. Fan, J. Fu, A. Collins, and Y. Zhao, “The effect of the shape of nanorod arrays on the nanocarpet effect,” Nanotechnology 19(4), 045713–045721 (2008). [CrossRef]
  24. S. J. Jang, Y. M. Song, J. S. Yu, C. I. Yeo, and Y. T. Lee, “Antireflective properties of porous Si nanocolumnar structures with graded refractive index layers,” Opt. Lett. 36(2), 253–255 (2011). [CrossRef] [PubMed]
  25. S. J. Jang, Y. M. Song, C. I. Yeo, C. Y. Park, J. S. Yu, and Y. T. Lee, “Antireflective property of thin film a-Si solar cell structures with graded refractive index structure,” Opt. Express 19(S2Suppl 2), A108–A117 (2011). [CrossRef] [PubMed]
  26. C. F. R. Mateus, M. C. Y. Huang, L. Chen, C. J. Chang-Hasnain, and Y. Suzuki, “Broad-band mirror (1.12-1.62 µm) using a subwavelength grating,” IEEE Photon. Technol. Lett. 16(7), 1676–1678 (2004). [CrossRef]
  27. L. Zeng, Y. Yi, C. Hong, J. Liu, N. Feng, X. Duan, L. C. Kimerling, and B. A. Alamariu, “Efficiency enhancement in Si solar cells by textured photonic crystal back reflector,” Appl. Phys. Lett. 89(11), 111111 (2006). [CrossRef]
  28. O. Blum, I. J. Fritz, L. R. Dawson, A. J. Howard, T. J. Headley, J. F. Klem, and T. J. Drummond, “Highly reflective, long wavelength AlAsSb/GaAsSb distributed Bragg reflector grown by molecular beam epitaxy on InP substrate,” Appl. Phys. Lett. 66(3), 329–331 (1995). [CrossRef]

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