Visible light emission from porous silicon under optical and electrical excitation

The main characteristics of porous silicon and the different charge exchanges involved in the formation of the material upon silicon anodisation in concentrated HF electrolytes are shortly recalled. The main features of the photoluminescence in the visible range which is observed at room temperature from high porosity layers are described. It is shown that the visible light emission can be analysed as the result of the quantum confinement of photogenerated charge carriers in the nanoscale crystallites which form the material. The electroluminescence which is obtained when the porous layer is in contact with an electrolyte is described in more details. It is shown that light emission can be observed either under anodic polarisation, but with a simultaneous oxidation of the layer, or under cathodic polarisation if a strong oxidising species is added to the electrolyte. In these conditions, a selective excitation of the material can be achieved, which leads to a voltage tunable electroluminescence signal. In a similar manner, the application of a polarisation can lead to a reversible, highly contrasted and energy-selective quenching of the porous layer photoluminescence.