Optical absorption evidence of a quantum size effect in porous silicon

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Abstract
This study presents optical transmission measurements performed on free‐standing homogeneous porous silicon (PS) films of different porosities and substrate doping levels. The absorption coefficient curves deduced from these measurements, taking into account the total quantity of matter in the PS film, exhibit significant blue shift (up to 500 meV). These shifts, well correlated with the crystallite size variations with porosity and substrate doping observed by electron microscopy and gas adsorption experiments, are attributed to quantum size effects in the silicon microcrystallites.