Antireflection Coating for MWIR on Calcium Fluoride Using Ion-Assisted E-Beam Deposition

Abstract

This research outlines the design, analysis, and fabrication of a multilayer anti-reflective coating on a calcium fluoride (CaF2) substrate, specifically for mid-wavelength infrared uses, employing the ion-assisted electron-beam evaporation method. A 2-layered multilayer structure in the form of SiO2/Ge was created on CaF2, consisting of low refractive index silicon dioxide (SiO2) and high refractive index germanium (Ge) thin films with a total thickness below 1 μm. The design was optimized for the 3.6-4.9 μm MWIR range, and an average transmission of 98.39% and an average reflectance of 0.93% were simulated at a broadband spectral width of 1300 nm. After the fabrication process using the ion-assisted physical vapour deposition (IAPVD) technique, the experimental results showed an average transmission of 98.13% and a reflectance value of 1.19% within the 3.6-4.9 μm range. The simulation design and experimental results were found to be very close to each other, with a difference of only 0.26%. This work provides a high-efficiency solution for AR coatings in the MWIR region on CaF2 surfaces. To our knowledge, the Ge/SiO2 multilayer structure on CaF2 has not been reported before in the literature and the results obtained will be an alternative for CaF2-based optical systems.

Keywords

• Mid-wave infrared (MWIR)
• Calcium fluoride
• Optical thin films
• Anti-reflective coating
• Ion-assisted e-beam deposition

References

1. [1]. Raut, H. K., Ganesh, V. A., Nair, A. S., Ramakrishna, S. 2011. Anti-reflective coatings: A critical, in-depth review. Energy & Environmental Science; 4(10): 3779-3804. doi: 10.1039/C1EE01297E.
2. [2]. Ji, C., et al. Recent Applications of Antireflection Coatings in Solar Cells. Photonics; 9(12). doi: 10.3390/photonics9120906.
3. [3]. Bouhafs, D., Moussi, A., Chikouche, A., Ruiz, J. M. 1998. Design and simulation of antireflection coating systems for optoelectronic devices: Application to silicon solar cells. Solar Energy Materials and Solar Cells; 52(1): 79-93. doi: 10.1016/S0927-0248(97)00273-0.
4. [4]. Chen, D. 2001. Anti-reflection (AR) coatings made by sol–gel processes: A review. Solar Energy Materials and Solar Cells; 68(3): 313-336. doi: 10.1016/S0927-0248(00)00365-2.
5. [5]. Kaminski, P. M., Lisco, F., Walls, J. M. 2014. Multilayer Broadband Antireflective Coatings for More Efficient Thin Film CdTe Solar Cells. IEEE Journal of Photovoltaics; 4(1): 452-456. doi: 10.1109/JPHOTOV.2013.2284064.
6. [6]. Yenisoy, A., Yeşilyaprak, C., Tüzemen, S. 2019. High efficient ultra-broadband anti-reflection coating on silicon for infrared applications. Infrared Physics & Technology; 100: 82-86. doi: 10.1016/j.infrared.2019.05.014.
7. [7]. Bhatt, M., Nautiyal, B. B., Bandyopadhyay, P. K. 2010. High efficiency antireflection coating in MWIR region (3.6–4.9 μm) simultaneously effective for Germanium and Silicon optics. Infrared Physics & Technology; 53(1): 33-36. doi: 10.1016/j.infrared.2009.08.006.
8. [8]. Valiei, M., Shaibani, P. M., Abdizadeh, H., Kolahdouz, M., Asl Soleimani, E., Poursafar, J. 2022. Design and optimization of single, double and multilayer anti-reflection coatings on planar and textured surface of silicon solar cells. Materials Today Communications; 32: 104144. doi: 10.1016/j.mtcomm.2022.104144.

9. [9]. Kala, M. B., Bandyopadhyay, P. K., Nautiyal, B. B. 2012. Thorium free antireflection coating in MWIR region on Silicon optics. Infrared Physics & Technology; 55(5): 409-411. doi: 10.1016/j.infrared.2012.05.005.
10. [10]. Amirzada, M. R., Khan, Y., Ehsan, M. K., Rehman, A. U., Jamali, A. A., Khatri, A. R. Prediction of Surface Roughness as a Function of Temperature for SiO2 Thin-Film in PECVD Process. Micromachines; 13(2). doi: 10.3390/mi13020314.
11. [11]. Melcher, F., Buchholz, P. 2014. Germanium. In: Gunn, A. G. (ed.) Critical Metals Handbook; Wiley, pp. 177-203.
12. [12]. Harris, D. C. 1999. Materials for Infrared Windows and Domes: Properties and Performance. SPIE Press.
13. [13]. Thomas, I. M. 1988. Porous fluoride antireflective coatings. Applied Optics; 27(16): 3356-3358. doi: 10.1364/AO.27.003356.
14. [14]. Deng, C.-Z., et al. 2019. Two-pair multilayer Bloch surface wave platform in the near- and mid-infrared regions. Applied Physics Letters; 115(9): 091102. doi: 10.1063/1.5101008.
15. [15]. Yan, J., Syoji, K., Tamaki, J. I. 2003. Crystallographic effects in micro/nanomachining of single-crystal calcium fluoride. Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena; 22(1): 46-51. doi: 10.1116/1.1633770.
16. [16]. Çetin, N. E., et al. 2013. The structural, optical and morphological properties of CaF2 thin films by using Thermionic Vacuum Arc (TVA). Materials Letters; 91: 175-178. doi: 10.1016/j.matlet.2012.07.086.
17. [17]. Zambrano, D. F., et al. 2021. Mechanical and microstructural properties of broadband anti-reflective TiO2/SiO2 coatings for photovoltaic applications fabricated by magnetron sputtering. Solar Energy Materials and Solar Cells; 220: 110841. doi: 10.1016/j.solmat.2020.110841.
18. [18]. Varade, A., Krishna, A., Reddy, K. N., Chellamalai, M., Shashikumar, P. V. 2014. Diamond-like Carbon Coating Made by RF Plasma Enhanced Chemical Vapour Deposition for Protective Antireflective Coatings on Germanium. Procedia Materials Science; 5: 1015-1019. doi: 10.1016/j.mspro.2014.07.390.
19. [19]. Choi, W. S., Kim, K., Yi, J., Hong, B. 2008. Diamond-like carbon protective anti-reflection coating for Si solar cell. Materials Letters; 62(4): 577-580. doi: 10.1016/j.matlet.2007.06.019.
20. [20]. Duris, M., Deubel, D., Bodiou, L., Vaudry, C., Keromnes, J. C., Charrier, J. 2021. Fabrication of Ge-ZnS multilayered optical filters for mid-infrared applications. Thin Solid Films; 719: 138488. doi: 10.1016/j.tsf.2020.138488.
21. [21]. Zhu, Z., et al. 2023. Scratch-resistant antireflective coating for mid-wave infrared band. Infrared Physics & Technology; 133: 104807. doi: 10.1016/j.infrared.2023.104807.
22. [22]. Yenisoy, A., Yesilyaprak, C., Ruzgar, K., Tuzemen, S. 2019. Ultra-broad band antireflection coating at mid wave infrared for high efficient germanium optics. Optical Materials Express; 9(7): 3123-3131. doi: 10.1364/OME.9.003123.
23. [23]. Dogan, Y., Erdogan, İ., Altuntepe, A. 2024. Design and fabrication of highly efficient antireflective coating in MWIR on germanium using ion-assisted e-beam deposition. Optical Materials; 157: 116362. doi: 10.1016/j.optmat.2024.116362.
24. [24]. Awasthi, S., Nautiyal, B. B., Kumar, R., Bandyopadhyay, P. K. 2012. Multi-spectral antireflection coating on zinc sulphide simultaneously effective in visible, eye safe laser wavelength and MWIR region. Infrared Physics & Technology; 55(5): 395-398. doi: 10.1016/j.infrared.2012.06.003.
25. [25]. Lemarquis, F., Marchand, G., Amra, C. 1998. Design and manufacture of low-absorption ZnS–YF3 antireflection coatings in the 3.5–16-μm spectral range. Applied Optics; 37(19): 4239-4244. doi: 10.1364/AO.37.004239.
26. [26]. Yao-ping, Z., Jun-qi, F., Hong, X. 2012. Anti-reflection coating on calcium fluoride substrate using ion-assisted deposition. In: Proceedings of SPIE; 8416: 84161Q. doi: 10.1117/12.976048.
27. [27]. Yenisoy, A., Tüzemen, S. 2020. Development of high efficient and ultra-broadband antireflection coating on calcium fluoride for electro-optical applications. Surface Engineering; 36(4): 364-370. doi: 10.1080/02670844.2019.1644936.
28. [28]. Michael, E. C. 2001. Challenges in IR optics. In: Proceedings of SPIE; 4369: 649-661. doi: 10.1117/12.445327.
29. [29]. Malitson, I. H. 1963. A Redetermination of Some Optical Properties of Calcium Fluoride. Applied Optics; 2(11): 1103-1107. doi: 10.1364/AO.2.001103.
30. [30]. Retherford, R. S., Sabia, R., Sokira, V. P. 2001. Effect of surface quality on transmission performance for (111) CaF2. Applied Surface Science; 183(3): 264-269. doi: 10.1016/S0169-4332(01)00587-6.
31. [31]. Jacob, R., Sergeev, D., Yazhenskikh, E., Müller, M. 2023. Evaluation of the calcium chloride-calcium fluoride system for high temperature thermal energy storage. Journal of Energy Storage; 72: 108521. doi: 10.1016/j.est.2023.108521.
32. [32]. Choi, J. H., Na, H., Park, J., Kim, H.-J. 2019. Plasma corrosion resistance of aluminosilicate glasses containing Ca, Y and B under fluorocarbon plasma with Ar+. Journal of Non-Crystalline Solids; 521: 119498. doi: 10.1016/j.jnoncrysol.2019.119498.
33. [33]. Bezuidenhout, D. F. 1997. Calcium Fluoride (CaF2). In: Palik, E. D. (ed.) Handbook of Optical Constants of Solids; Academic Press: Burlington, pp. 815-835.
34. [34]. Zhan, J., Guo, Y., Wang, H. 2024. Electro-plastic effect on the indentation of calcium fluoride. International Journal of Mechanical Sciences; 261: 108693. doi: 10.1016/j.ijmecsci.2023.108693.
35. [35]. Lee, H. W. 1926. The Hartmann formula for the dispersion of glass. Transactions of the Optical Society; 28(3): 161. doi: 10.1088/1475-4878/28/3/303.