ELECTROLUMINESCENCE OF HEAVILY-DOPED P-TYPE POROUS SILICON UNDER ELECTROCHEMICAL OXIDATION IN THE POTENTIOSTATIC REGIME

Visible light emission is obtained during the anodic oxidation of heav ily doped p-type porous silicon layers, with similar characteristics t o the electroluminescence observed on lightly doped substrates. This i ndicates that the coarser structure of the heavily doped layers also p resents a thinner structure, with crystallites of quantum sizes respon sible for the emission. In this paper, the electroluminescence is stud ied in potentiostatic conditions, under either fixed or scanned potent ials. Some reversibility in the spectral changes versus potential vari ations can be evidenced by selecting correctly the scanning conditions and the potential values. The results allow one to conclude that the electroluminescence spectral evolution is mostly determined by the app lied polarisation and can be attributed to the selectivity of the carr iers injection into the quantum-size crystallites of the material. The electroluminescence vanishing which is observed in the second part of the anodic oxidation regime seems related in the higher potential ran ge to some depassivation of the porous silicon surface. For the lower potential range, owing to the oxide growth, the emission stops when th e polarisation is no longer enough to inject holes into the confined c rystallites.