Formation mechanism and pore size control of light-emitting porous silicon

The mechanisms of silicon dissolution and pore formation during the formation of porous silicon layers (PSLs) are investigated in the HF-water electrolyte solution. As HF concentration increases in the electrolyte, the depth of pores increases while the pore diameter decreases. It is found that hydroxide ion ( OH - ) plays an apparently significant role in the reaction with silicon. The formation of silicon oxide is observed on the silicon surface during PSL formation. The dissolution mechanism of silicon is presented, based on spectroscopic analyses for the porous silicon surface. The area of initially formed silicon oxide on the silicon wafer surface determines the pore diameter. With increasing amount of OH - ions, or equivalently decreasing HF concentration, the thickness of the silicon walls between pores is reduced, revealing the blue shift of photoluminescence energy due to the quantum size effect.