In Ukrainian

Abstract

The purpose of this article is to present theoretical calculations of the optical spectra of periodic silicon nanostructures dependent on their length. For calculations, the structure with silicon nanowires with a constant diameter and period was simulated. The diameter of the nanowires is 80 nm, and the structure period is 100 nm. The dependence of absorption, reflection and transmission spectra on the length of nanowires (500–5000 nm) was investigated. For theoretical studies, the Maxwell equation was solved by the finite difference method in the time domain (FDTD). This method can be applied precisely to general electromagnetic structures, including free-form particles. The advantage of this method is the simplicity and the capability to obtain results for a wide range of wavelengths in single calculation, as well as the capability to specify the properties of materials at any point of the calculation grid, which allows us to consider anisotropic, dispersive and nonlinear environments. At the same time, the FDTD method can be very resource-intensive, especially when simulating complex structures. This method requires from 10 to 30 points per wavelength, and small wavelengths determine the very high sampling frequency. This leads to cumbersome calculations, especially in three dimensions. To simplify calculations, the problem was carried out in two-dimensional form. It is shown that for these parameters of the structure, the reflection coefficient does not depend on the length of the nanowires, although by 30 % it is smaller than that in the solid silicon plate. The transmission coefficient decreases with the increase in the length of the nanowires, although at all calculated wavelengths it remains higher than that in the silicon wafer. It is shown that in the visible region of the spectrum, the absorption coefficient is significantly higher and with the increase of the length of nanowires, an expansion of absorption spectra is observed, indicating an increase in the absorption range of sunlight. It is shown that the use of silicon nanostructures as solar cells is an important and perspective direction of research.