Photodissolution and photoluminescence quenching of porous silicon in HF

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Abstract
A photodissolution process occurs when porous silicon samples, immersed in HF solutions, are continuously illuminated. In situ reflectivity measurements allow us to deduce the time evolution of: the optical index; the thickness of the porous layer; and the number of atoms dissolved per unit time, which is found to be proportional to the specific surface of the sample exposed to HF. We have also compared photoluminescence properties of porous samples dried and immersed in HF under continuous and pulsed UV excitations. Photoluminescence can be totally or partially quenched and lifetimes are at least two orders lowered in HF solutions. The relevant parameter of the quenching is again the specific surface of porous silicon in contact with the liquid, suggesting that photoluminescence quenching and photodissolution have the same origin.