LIGHT-EMISSION FROM POROUS SILICON UNDER PHOTOEXCITATION AND ELECTROEXCITATION

With its large, inhomogeneously broadened optical transitions porous s ilicon offers new, interesting fluorescence line narrowing effects. Ca thodic current transfer at lightly doped n-type porous layers in conta ct with an aqueous solution exhibits reversible, highly contrasted vol tage-selective quenching of the photoluminescence (QPL) for a voltage variation of only about 500 mV. A spectral blue shift along with a nar rowing of the linewidth accompanies the observed strong QPL. It is exp lained 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 per sulfate solutions shows a tuning as large as 270 nm for an extermal bi as variation of 0.6 V. The study of the EL behavior as a function of t he external voltage and the persulfate ion concentration proves that w hile the amplitude of the EL is proportional to the intensity of the e xchanged current, the spectral position is only determined by the appl ied voltage. It is explained by the double selectivity of electron and hole injection.