FORMATION MECHANISM AND PORE SIZE CONTROL OF LIGHT-EMITTING POROUS SILICON

The mechanisms of silicon dissolution and pore formation during the fo rmation of porous silicon layers (PSLs) are investigated in the HF-wat er electrolyte solution. As HF concentration increases in the electrol yte, the depth of pores increases while the pore diameter decreases. I t is found that hydroxide ion (OH-) plays an apparently significant ro le in the reaction with silicon. The formation of silicon oxide is obs erved on the silicon surface during PSL formation. The dissolution mec hanism of silicon is presented, based on spectroscopic analyses for th e porous silicon surface. The area of initially formed silicon oxide o n the silicon wafer surface determines the pore diameter. With increas ing amount of OH- ions, or equivalently decreasing HF concentration, t he thickness of the silicon walls between pores is reduced, revealing the blue shift of photoluminescence energy due to the quantum size eff ect.