CC BY
3The 30th International Conference on Advanced Laser Technologies LD-P-5
ALT'23
Polarization-sensitive infrared spectroscopy of thin amorphous
silicon films with LIPSS
S. Zabotnov1, D. Shuleiko1, E. Kuzmin2, P. Pakholchuk2, L. Volkovoynova3, A. Serdobintsev3,
P. Kashkarov1
1-Lomonosov Moscow State University, Faculty of Physics, 1/2 Leninskie Gory, Moscow, 119991, Russia 2- P.N. Lebedev Physical Institute of RAS, 53 Leninsky Ave., Moscow, 119991, Russia 3- Saratov State University, 83 Astrakhanskaya St., Saratov, 410012, Russia
Modern challenges of photonics and nanoelectronics require designing new compact planar elements for integrated photonic circuits. Such systems usually are based on various thin semiconductor films. Therefore, fast and scalable techniques to make micro- and nanostructures in the thin films are actively developing now. Different multi-stage lithography techniques are widely used. Additionally, direct laser writing (DLW) approaches allow fabrication of photonic and electronic micro- and nanocomponents with desirable properties in one step. In particular, laser-induced periodic surface structures (LIPSS) can be created with femtosecond laser irradiation. One of the reasons of LIPSS arising is intensive photoexcitation of electron-hole plasma with following surface plasmon-polariton generation at semiconductor surface [1,2]. Such surface electromagnetic waves give a contribution to the relief modulation with the wavelength- and subwavelength periods.
Thin amorphous silicon films look promising for the DLW technique. So, LIPSS formation in them leads to noticeable optical [3] and electrophysical anisotropy [4] in plane of a sample.
Herein, we describe our experiment with thin amorphous silicon films (1.0 ^m), including the films covered with a 10 nm aluminum layer, irradiated with femtosecond laser pulses (515 and 1030 nm, 300 fs). As a result, LIPSS were fabricated, and they covered areas up to 2x2 mm2. Structural features of irradiated surfaces were examined by optical and scanning electron microscopy. All LIPPS are gratings oriented perpendicular to the laser beam polarization and have periods close to the wavelength. The observed LIPSS formation is well explained with the plasmon-polariton mechanism and the so-called Sipe-Drude theory [1,5]. Surface periodicity may lead to artificial anisotropy according to the generalized Bruggeman model [6]. To examine the anisotropy, we studied our samples by Fourier-transform infrared spectroscopy in the range of 500-6500 cm-1 where silicon possesses relatively low absorption. The measured reflectance spectra are characterized by interference in the thin silicon films. The spectra are different for various polarization of the incident light. An analysis of the values of interference extremums and their spectral positions allowed to estimate the dichroism and birefringence values, respectively. The best results were obtained in the spectral region of 1.9-2.7 ^m: the dichroism is 0.12 (the difference between the absorption coefficients) and the birefringence is 0.2 (the difference between the refractive indices for the ordinary and extraordinary waves). These values look sufficient to further designing polarization-sensitive planar devices for the near infrared region.
The investigation was funded by the Russian Science Foundation grant # 22-19-00035, https://rscf.ru/proj ect/22-19-00035/.
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