Porous silicon formation and other photoelectrochemical effects at silicon electrodes anodized in hydrofluoric acid

Illumination is an important parameter in the electrochemistry of silicon. A moderately doped (<1018 cm−3) n-type silicon electrode anodized in the dark is passivated against dissolution in HF due to the absence of holes which promote dissolution. Under illumination a current proportional to the light intensity is observed. This dependence of the current on the illumination enabled us to realize relief structures on the electrode surface without the use of standard photolithography. The photoassisted formation of macropores is another aspect of the photoelectrochemistry of silicon reported in this work. Many useful applications such as a silicon based capacitor or photonic band gap materials in the infrared regime are based on photoelectrochemically etched macropores.