SURFACE PASSIVATION - A CRITICAL PARAMETER FOR THE VISIBLE LUMINESCENCE OF ELECTROOXIDIZED POROUS SILICON

It is shown that the passivation of the internal surface of pores determines not only the intensity but also the spectral dependence of the luminescence. Anodic oxidation is used as a method of passivation and thinning of the porous structure, it enables us to follow the evolution of the photoluminescence, decay times and electroluminescence. Since the room temperature luminescence is dominated by the non-radiative recombination on the surface, we introduce a model with two types of crystallites depending on their surface passivation. For the perfectly passivated crystallites, we describe the non-radiative recombination mechanism as carriers escaping by tunnelling through the surrounding potential barriers of the crystallite. This model is able to explain at the same time the PL and EL evolution during anodic oxidation as well as the form of the decay times and their wavelength dependence.