MECHANISM OF THE VISIBLE LUMINESCENCE IN POROUS SILICON

Highly efficient photoluminescence (PL) in the visible light range has been found in porous Si (PS). The quantum confinement model (QCM) for the PL mechanism although-h explains why the PL energy of PS is in the visible light range, it meets great difficulties in explaining blue and especially red shifts of the PL peak position of PS with varying temperature, pressure, anodic-etching conditions and post-treatments. Considering the rational parts of the previous models and also the contradictions between these models and experimental results, a new model is proposed in this work which explains qualitatively a lot of important experimental results without severe difficulties. We emphasize that there is a lack of nonradiative recombination centers inside the nanoscale Si unit and there is a much greater probability of radiative recombination through luminescence centers outside nanoscale Si units than through band to band transitions inside the nanoscale Si units and these two factors explain why PS has a highly efficient PL. The suggested model may also be applicable to some other Si-based luminescent materials other than PS.