Wide-band ‘black silicon’ with atomic layer deposited NbN

Abstract

Antireflection surfaces are often utilized in optical components to reduce undesired reflection and increase absorption. We report on black silicon (b-Si) with dramatically enhanced absorption over a broad wavelength range (250-2500 nm) achieved by applying a 10-15 nm conformal coating of NbN with atomic layer deposition (ALD). The improvement is especially pronounced in the near infrared (NIR) range of 1100-2500 nm where absorption is increased by >90%. A significant increase of absorption is also observed over the ultraviolet range of 200-400 nm. Preceding NbN deposition with a nanostructured ALD AlO (n-AlO) coating to enhance the NbN texture was also examined. Such texturing further improves absorption in the NIR, especially at longer wavelengths, strong absorption up to 4-5 μm wavelengths has been attested. For comparison, double side polished silicon and sapphire coated with 10 nm thick NbN exhibited absorption of only ∼55% in the NIR range of 1100-2500 nm. The results suggest a positive correlation between the surface area of NbN coating and optical absorption. Based on the wide-band absorption, the presented NbN-coated b-Si may be an attractive candidate for use in e.g. spectroscopic systems, infrared microbolometers.

Recent Progress of Black Silicon: From Fabrications to Applications

“…The average reflectivity of the material at different angles from 350 nm to 1000 nm was below 10%. In 2018, K. Isakov et al [67] fabricated broad-band absorption black silicon for niobium nitride deposition at the atomic layer using ICP-RIE technology. Black silicon was fabricated by etching the silicon surface with a mixture of SF 6 and O 2 gas at −110 • C. In the spectral region of 1100~2500 nm, the sample of niobium nitride layer coated with 15 nm achieved high absorption of 97%~99%.…”

Mg$_2$Si is the new black: introducing a black silicide with $>$95% average absorption at 200-1800 nm wavelengths

“…However, the former material clearly demonstrates slightly increased VIS reflection with specific silicide related spectral feature at 500 nm (2.5 eV) resulted from first direct interband optical transition in Mg 2 Si 32 . This fact suggests that Mg 2 Si nanoflakes provide enough area for the sur- 2a) and compared to state-of-the-art black surface structures 13,14,16,20,[33][34][35] (Figure 2c). Optical absorption spectra (A) calculated as 1-T-R demonstrate that optical properties of the b-Si changed drastically after Mg 2 Si deposition.…”

“…[34] 13,14,16,20,[33][34][35] Significantly, the wide range optical absorption performance of the black silicide is compared with state-of-theart approaches to enhance NIR efficiency of the b-Si as shown in Fig. 2c.…”

“…Thus, it is expected that near-infrared (NIR) absorbing layer deposited above b-Si surface would result in extension of its spectral blackness. So far, b-Si structures have been modified via thin film or nanoparticles deposition, formation of the hierarchical carbon-based nanostructures atop or pulsed laser postprocessing [13][14][15][16][17][18][19][20][21] . To date, practical use of the outlined approaches is limited by the low cost-efficiency factor resulted from the expensive deposition methods applied (atomic-layer deposition, molecular-beam epitaxy, etc. )…”

“…(b) Black silicide morphology reconstruction basing on the STEM HAADF image for modeling normalized squared electric-field amplitude distribution (E 2 /E 2 0 ) at 1300 nm pump wavelength of the Mg 2 Sicovered and bare b-Si structures. (c) Survey of operating wavelength range and averaged optical absorption of the produced black silicide and several representative b-Si structures reported in13,14,16,20,[33][34][35] .…”