Spectral diffuse scattering in porous silicon

Abstract

Scattering-enhanced absorption in silicon is well-known and has been applied in a variety of silicon-based optoelectronic devices such as photodetectors, solar cells and sensors. However, the actual diffuse scattering mechanism and property in nano-structured silicon remain elusive because of the complicated surface morphologies. In this paper, we study diffuse scattering in high resistivity porous silicon samples in the spectral region below their bandgap, where the surface scattering is accessible with minimum influence from material absorption. The spectral measurements reveal that the diffuse scattering monotonously decreases with wavelength and increases with the pore size, similar to the classical Rayleigh scattering. However, the scattered intensity is inversely proportional to λn with n = 1-3.7 instead of the classical 4. Also, an asymmetry between the forward diffuse transmission and backward diffuse reflection is observed. The hemispherical diffuse transmission is larger than the diffuse reflection by a factor of 2-4. This asymmetry in scattering is supported with numerical simulations, which suggest that the nanopores favor forward light scattering into the substrate. These results are helpful in further understanding the interaction between light and nano-structured silicon.