Bright visible electroluminescence has been evidenced during the anodic oxidation of ptype porous silicon films in aqueous electrolytes. It is shown that in galvanostatic conditions, two very different light emission regimes can be obtained depending on the anodic potential. At low potentials, during the progressive oxidation of the pore walls, the emission spectra present a maximum in the red-orange wavelengths : the emitted intensity increases with the oxidation level, while the maximum is shifted towards shorter wavelengths. This emission vanishes when the anodic potential starts to increase more rapidly. Upon increasing polarizations, a second regime of light emission with a spectrum centered in the green wavelength range is observed. In this case, the spectrum and the intensity are both stable under extended anodization.
This last regime which is explained by carrier injection into the anodic oxide is not specific of the porous character of samples. On the contrary, the red-orange emission is shown to be closely related to the photoluminescence properties of the porous layer. A phenomenologic model is proposed, which analyses the electroluminescence characteristic dependence upon the oxidation level in terms of competition between the enhancement of the radiative process and the progressive electrical cut-off of the emitting crystallites.