Optical Properties of Porous Silicon Layers Formed by Electroless Photovoltaic Etching

An approach to forming porous silicon (PSi) has been developed that uses a closed-circuit anodic system under Xe lamp illumination without an external voltage. A HF/H2O2 electrolyte makes it possible to form a highly roughened PSi layer on an n-type Si substrate. Bright yellow photoluminescence with a peak at ∼600 nm was observed from such PSi layers. The absorbance in the visible−UV region of the PSi was also found to be about two orders larger than that of anodic PSi layers conventionally formed on p-type Si substrates. Scanning electron microscopy revealed that the porous structure has many zigzag pillars. The PSi formation mechanism is explained by taking into consideration the photovoltaic effect and the surface energy-band diagram at the n-Si/electrolyte interface.