Nanostructured surface

Simulation of optical properties of silicon periodic nanostructure for solar cells
Havryliuk O.O., Semchuk O.Yu.
Chuiko Institute of Surface Chemistry of the NAS of Ukraine. 17 Ganeral Naumova Str., Kyiv-03164, Ukraine. 
E-mail: gavrylyuk.oleksandr@gmail.com

Silicon nanostructures such as porous silicon, silicon nanotubes and silicon nanowires (SiNWs) have recently attracted considerable attention because of their interesting physical properties as compared to bulk silicon [1].
In nanowired solar cell applications SiNW arrays vertically aligned to the substrate demonstrate broadband optical absorption due to strong light trapping by multiple scattering of the incident light.  Since the typical geometric factors of SiNWs, including wire diameter, length, and periodicity, are known to significantly affect the optical properties, a coefficient, optimized technique is critically needed to precisely control the major dimensional variables for solar cell applications [2].
Using numerical method FDTD (Finite-Difference Time-Domain) was calculated distribution  of the electric and magnetic fields on the surface nanostructure  and absorptace, transmittance and reflectance spectra. The FDTD method is a state-of-the-art method for solving Maxwell's equations in complex geometries. In modern implementations of the FDTD method, an explicit second-order accuracy scheme is used for the step of time Δt and spatial Δx, Δy, Δz of sampling proposed by Yee [3].
The solution of the Maxwell's equation made it possible to calculate the absorption spectrum for the investigated structure. It is shown that nanostructures on the surface of silicon improve its optical characteristics.

1.	Khorasaninejad M., Swillam M.A., Pilla K., Saini S.S. Silicon nanowire arrays with enhanced optical properties // Optics Letters.-2012.-37, N 20.-P.4194-4196.  
2.	Jin-Young Jung, Zhongyi Guo, Sang-Won Jee, Han-Don Um, Kwang-Tae Park, Jung-Ho Lee. A strong antireflective solar cell prepared by tapering silicon nanowires // Optics Express.-2010.-18, N S3.-P. A286-A292.
3.	Yee K.S. Numerical solution of initial Boundary Value Problems involving Maxwell's equations in isotropic media // IEEE Trans. Antennas and Propagation.-1996.-14.-P. 302-307.