Laser-induced formation of porous silicon

The mechanism of photoelectrochemical porous silicon formation in fluoride solutions under laser illumination and dark conditions has been investigated. Experiments were performed in a PTFE cell with a plastic window to allow the laser path to be horizontal and the silicon electrode to be in a vertical position inside the cell. Dark and illuminated anodic and cathodic current-voltage (I-V) curves were both measured in real time by chopping the laser beam. N-type wafers of resistivities 0.001 to 22 Ω · cm have been investigated for various conditions of illumination intensity and polarization. We focused our attention on relatively low illumination intensities ∼ 10−5–10−8 W/mm2 and high HF concentration. By measuring the dissolution rate and the photogenerated current we estimated that the main reaction path requires two holes for each Si atom as: image. The utilization of this technique for direct projection printing of porous Si images of 10 μm resolution was demonstrated.