The growing use of optical coatings in the fields of electronics defense/security and solar energy has led to an increased demand for antireflective and reflective coatings. In this study, we designed and fabricated antireflective coatings comprised of erbium oxide (Er
2O
3), silicon dioxide (SiO
2), and alternating layers of Er
2O
3 and SiO
2 on different substrate materials (silicon, fused silica and sapphire). Three coating designs were simulated on each substrate by using the
OpenFilters1 program: (1) a single-layer coating of Er
2O
3 or SiO
2, (2) a double-layer coating of SiO
2/Er
2O
3, and (3) a quadruple-layer alternating coating of SiO
2/Er
2O
3/SiO
2/Er
2O
3. The coatings were deposited on the substrates under controlled parameters using reactive magnetron sputtering (76 mm diameter targets and 1 Amp currents) in order to achieve the lowest reflectance in the infrared dual-band wavelengths of 1.9-2.5 µm and 3.6-5.0 µm. The quadruple coatings exhibited superior properties with 1.4% average reflectance when Er
2O
3 was deposited using 3 vol.%. O
2 atmosphere and a substrate bias of -60 V. Under these conditions, a high deposition rate of 100 nm/min was achieved (similar to the deposition rate of metallic erbium coatings). The Er
2O
3 coatings were dense and contained a mixture of cubic and monoclinic phases, a maximum compressive stress of 1 GPa and a refractive index of 1.82. In contrast, the SiO
2 coatings were deposited with an amorphous structure at a typically low deposition rate of ~2-4 nm/min under the same deposition parameters, with a maximum compressive stress of 0.2 GPa and a refractive index of 1.49.
1Stéphane Larouche and Ludvik Martinu, OpenFilters: open-source software for the design, optimization, and synthesis of optical filters, Applied Optics, Vol. 47, Issue 13, pp. C219-C230 (2008)