Light modulation with porous silicon

A large thermal light modulation effect, based on absorption modulation, is demonstrated in highly doping p-type porous silicon. The absorption is measured by monitoring the transmitted intensity of a probe beam through a self-standing porous silicon film, and the modulation of absorption is obtained by exciting the sample with a second optical beam. The modulation has also been investigated by photoluminescence excitation technique. A novel model based on temperature variations induced by the second optical beam is developed, and the consistency with the experimental data is demonstrated. Further evidence of the thermal interpretation is provided by measuring the time decay constant of the modulation effect and the dependence of the modulation on the average intensity of the second beam. It is also shown that the thermal modulation effect is not observable in low doping p-type porous silicon. A systematic study of photoluminescence properties of both low and high doping p-type porous silicon depending on the sample preparation conditions is also presented and discussed.