Structural, optical, and mechanical properties of Al₂O₃, SiO₂, and HfO₂ materials prepared by plasma-enhanced atomic layer deposition (PEALD) were investigated. Residual stress poses significant challenges for optical coatings since it may lead to mechanical failure, but in-depth understanding of these properties is still missing for PEALD coatings. The tensile stress of PEALD alumina films decreases with increasing deposition temperature and is approximately 100 MPa lower than the stress in thermally grown films. It was associated with incorporation of -OH groups in the film as measured by infrared spectroscopy. The tensile stress of hafnia PEALD layers increases with deposition temperature and was related to crystallization of the film. HfO₂ nanocrystallites were observed even at 100°C deposition temperature with transmission electron microscopy. Stress in hafnia films can be reduced from approximately 650 MPA to approximately 450 MPa by incorporating ultrathin Al₂O₃ layers. PEALD silica layers have shown moderate stress values and stress relaxation with the storage time, which was correlated to water adsorption. A complex interference coating system for a dichroic mirror (DCM) at 355 nm wavelength was realized with a total coating thickness of approximately 2 μm. Severe cracking of the DCM coating was observed, and it propagates even into the substrate material, showing a good adhesion of the ALD films. The reflectance peak is above 99.6% despite the mechanical failure, and further optimization on the material properties should be carried out for demanding optical applications.

Abstract:We have investigated the suitability of atomic layer deposition (ALD) for SiO 2 optical coatings and applied it to broadband antireflective multilayers in combination with HfO 2 as the high refractive index material. SiO 2 thin films were successfully grown using tris [dimethylamino]silane (3DMAS), bis [diethylamino]silane (BDEAS) with plasma activated oxygen as precursors, and the AP-LTO 330 precursor with ozone, respectively. The amorphous SiO 2 films show very low optical losses within a spectral range of 200 nm to 1100 nm. Laser calorimetric measurements show absorption losses of 300 nm thick SiO 2 films of about 1.5 parts per million at a wavelength of 1064 nm. The films are optically homogeneous and possess a good scalability of film thickness. The film surface porosity -which correlates to a shift in the transmittance spectra under vacuum and air conditions -has been suppressed by optimized plasma parameters or Al 2 O 3 sealing layers. and TiO 2 multilayers for applications as bandpass filters and antireflection coatings," Appl. Opt. 48(9), 1727-1732 (2009). 7. N. T. Gabriel, S. S. Kim, and J. J. Talghader, "Control of thermal deformation in dielectric mirrors using mechanical design and atomic layer deposition," Opt. Lett. 34(13), 1958-1960 (2009 4675-4685 (2012). 25. K. J. Hughes and J. R. Engstrom, "Nucleation delay in atomic layer deposition on a thin organic layer and the role of reaction thermochemistry," J.

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A normal-incidence light-trapping scheme relying on black silicon surface nanostructures for Si-based photoemissive detectors, operating in the IR spectral range, is proposed. An absorptance enhancement by a factor of 2–3 is demonstrated for technologically most relevant, ultrathin (2 nm–3 nm) PtSi rear layers on Si. It is shown that this increase can be translated into an equivalent increase in responsivity because of the absorption limitation of detector performance. Pd2Si/p-Si detectors with black silicon are suggested as promising candidates for room temperature detection in the third optical window with an expected external quantum efficiency in the range of 9%–14%.