LIGHT-EMISSION FROM POROUS SILICON UNDER PHOTOEXCITATION AND ELECTROEXCITATION

With its large, inhomogeneously broadened optical transitions porous silicon offers new, interesting fluorescence line narrowing effects. Cathodic current transfer at lightly doped n-type porous layers in contact with an aqueous solution exhibits reversible, highly contrasted voltage-selective quenching of the photoluminescence (QPL) for a voltage variation of only about 500 mV. A spectral blue shift along with a narrowing of the linewidth accompanies the observed strong QPL. It is explained either by a selective saturation or by a selective Auger effect, both due to carrier injection at energies determined by the applied voltage. The electroluminescence (EL) of porous silicon in aqueous persulfate solutions shows a tuning as large as 270 nm for an extermal bias variation of 0.6 V. The study of the EL behavior as a function of the external voltage and the persulfate ion concentration proves that while the amplitude of the EL is proportional to the intensity of the exchanged current, the spectral position is only determined by the applied voltage. It is explained by the double selectivity of electron and hole injection.