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2Light guiding nanostructures based on non-van-der-Waals
InGaS3 thin layers
A. Kuznetsov1'2*, E.S. Zavyalova2, P.A. Alexeev3, A.N. Toksumakov1, F.M. Maksimov1, V.M. Kondratev1, M.A. Anikina1,2, A.D. Bolshakov1,2,4
1-Moscow Institute of Physics and Technology, Institutskii per. 9, 141701, Dolgoprudny, Moscow region, Russia 2- Alferov University, Khlopina str., 8/3, 194021, St. Petersburg, Russia 3- Ioffe Institute, Polytekhnicheskaya st., 26, 194021, St. Petersburg, Russia 4- Yerevan State University, 1 AlexManoogian, 0025, Yerevan, Republic of Armenia
Today the search of novel optical materials for nanophotonics integrated circuits is under particular interest. One of the biggest problems in integrated photonics is the ways how to increase the surface packing density of the functional elements, which can be achieved using materials with high refractive index, operating in the range of shorter wavelengths than Si, for example in visible. InGaS3 is a semiconductor with a large bandgap (2.73 eV) and high refractive index (< 2.5) [1]. It is a novel material with hexagonal crystal lattice and layered structure but the origin of interlayer bonds is not van-der-Waals but covalent. Its inhomogeneous distribution all over the layer and low density per unit area makes it quite easy to separate the thin layers from each other by a variety of methods [1].
In this work we've investigated the influence of strip and slot waveguides geometry on its optical properties. We've used numerical simulations in Ansys Lumerical software (FDFD and FDTD algorithms) to develop the design of square, rectangle and slot waveguides and evaluate the influence of its longitudinal and lateral size on eigenmodes field distribution, optical loss, transmittance spectra etc. For strip waveguides we've demonstrated the designs for square, rectangle TE and TM cross-section geometry behind the cut-off (~70-100 nm), in the single- (~120-170 nm) and multimode regime (>250 nm). Waveguiding cut-off assigned to field delocalization was identified by effective refractive index dependencies from the lateral size. Transmittance spectra demonstrated both cut-off and InGaS3 intrinsic absorption (485-505 nm) ranges. Also several strip waveguides with cross-sections of 500x800 nm2 were fabricated using atomic-force lithography which have demonstrated broadband waveguiding from 630 up to 500 nm.
For the slot waveguides the gap modes were calculated (for 505 nm wavelength) in the range of strips lateral sizes, for different gaps (10-50 nm) and different underlayer thickness in the gap region. Calculations were provided in accordance with the strip waveguides case. Transmittance spectra also demonstrated the delocalization spectral range shift for different gap size which allows us to develop the bandpass or longpass optical filters. The obtained results open the possibility for fabrication of novel photonic devices based on InGaS3 thin layers.
[1] A.N. Toksumakov, et al, High-refractive index and mechanically cleavable non-van der Waals InGaS3, npj 2D Materials and
Applications, 6.1., pp. 85, (2022).
