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 dete rmines 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 evolutio n of the photoluminescence, decay times and electroluminescence. Since the room temperature luminescence is dominated by the non-radiative r ecombination on the surface, we introduce a model with two types of cr ystallites depending on their surface passivation. For the perfectly p assivated crystallites, we describe the non-radiative recombination me chanism as carriers escaping by tunnelling through the surrounding pot ential barriers of the crystallite. This model is able to explain at t he same time the PL and EL evolution during anodic oxidation as well a s the form of the decay times and their wavelength dependence.