Microstructure and Optical Properties of Black Silicon Layers

摘要

Black silicon structures were formed by etching of silicon substrates based on the surface structure chemical transfer method. Formed structures show gradient of material density in the nanocrystalline Si layer leading to ultralow spectral reflectance below 3% in wide spectral region. In study of the development of microstructure properties during the forming procedure the TEM images were used. Information abut the microstructure observed in the TEM images was analysed by the Abbott-Firestone method. By using this approach limiting conditions for the black silicon layer formation were obtained. Spectral reflectances of studied samples were modelled by using the effective medium theory. Multilayer theoretical model based on splitting the black silicon layer into 20 sublayers was constructed. Optical properties of each individual sublayer were described by using Bruggeman effective media theory combining Si, SiO_2 and void fractions. Gradual development of real and imaginary part of complex index of refraction was observed in the volume of black silicon layers. Results of optical analysis correspond to the microstructure development during sample forming.