Evaluation of the electrical conductivity of nano-porous silicon from photoluminescence and particle size distribution

This paper aims modelling and determining the electrical conductivity of nano-porous silicon (nano-PS) films. The latter were prepared by electrochemical etching monocrystalline silicon (c-Si) wafers in HF-based solutions for different values of the anodic current. The experimental values of the dc-electrical conductivity of nano-PS films were obtained using the dark current–voltage (I–V) characteristic of an Al/nano-PS/c-Si/Al type structure. The electrical conductivity of the PS films was theoretically estimated using the Bruggeman effective medium approximation (EMA) theory and by considering quantum size effects in small silicon particles. We give a comparative study between two different approaches. In the first one, we assume the PS layer to be formed of three phases: vacuum, oxide and c-Si nanocrystallites having the same mean size dimension (mean size value). In the second approach, we consider the nanocrystallites as being formed of multiple crystalline phases, depending on their size dimension. As a result, we found that in the case of the first simple approximation (three simple phases), theoretical data fit well the experimental results for small and medium porosities, and a discrepancy appears for porosities greater than 65%. However, in the case of multiple phases, theoretical values fit very well the experimental results for all porosities.